Daniel sent us this one, and it's got layers. He's been thinking about Jerusalem's Shabbat traffic drop and what it tells us about air pollution. That got him to Venice — a city that actually functions without cars, using waterways for everything from Amazon deliveries to ambulance speedboats. His question is: what other cities have serious internal waterway transit systems, and when you compare a bus to a fuel-efficient motorized boat, what's the actual pollution footprint? There's a lot to unpack here.
By the way, DeepSeek V four Pro is writing our script today. Which feels appropriate given we're talking about transport efficiency.
The AI down the road is handling this one. Alright, so where do we even start? Venice as the proof of concept, or the other canal cities?
Let's start with Venice, because Daniel's right — most people see it as a tourist museum, not a functioning city. But it is a functioning city. Sixty thousand people live in the historic center. They need groceries, they need ambulances, they need trash collection. All of it happens on water. The canal network is about forty-two kilometers of navigable waterways, and the Grand Canal alone handles something like two thousand commercial vessel movements a day.
Two thousand a day on one canal. That's not gondolas with accordion players. That's actual logistics.
The delivery infrastructure is surprisingly sophisticated. DHL has a dedicated Venice logistics center that transfers packages onto electric boats for the final mile. Amazon, like Daniel mentioned, uses cargo barges that dock at designated points, and then couriers use hand trucks to wheel deliveries through the narrow alleys. There's a company called Veneziana Gestione that handles most of the municipal waste collection — they have specialized garbage boats with hydraulic lifts that collect dumpsters right from canal-side collection points.
I want to pause on the garbage boats for a second, because that's where the romance of canal living meets reality. In most cities, a garbage truck rumbles down your street at six in the morning and you curse it. In Venice, it's a garbage boat. Does it just... float past your front door?
The boats navigate the smaller canals, and workers manually haul waste containers from buildings to the boat. It's actually more labor-intensive than truck-based collection, which is one of the hidden costs of a water-based city. But it works. The same company also handles recycling, with separate boats for glass, paper, and organic waste.
The ambulance situation Daniel mentioned — speedboat ambulances. That sounds made up, but it's completely real.
It's completely real. The Venice emergency medical service operates a fleet of rescue boats equipped with full life-support systems. They're built by specialized manufacturers, can hit about thirty knots, and they dock at hospital piers. The main hospital, Ospedale Civile, has a dedicated ambulance boat entrance. There's also a fire department that uses boats, and even the police have waterborne units. Every municipal service that would normally use a road vehicle has a water equivalent.
Venice proves the concept, but it's also a bit of a cheat. It was never retrofitted for boats — it was built before cars existed. The canals weren't an alternative transportation choice, they were the only option for centuries. What about cities that have deliberately built or maintained water transit alongside roads?
This is where it gets interesting, because there are more examples than people realize. The most obvious parallel is probably Bangkok. It's called the Venice of the East, and not just for aesthetic reasons. The khlong system — these are the canals — historically covered the city. A lot of them were filled in during the twentieth century to build roads, but a significant network remains, and it's used for actual transit. The Khlong Saen Saep boat service carries about sixty thousand passengers a day.
Sixty thousand daily riders on canal boats. That's a real transit system, not a tourist novelty.
It's raw, utilitarian transit. These are longtail boats with covered passenger sections, and they're fast. The operators use a distinctive stop system — you have to be paying attention because they don't always announce stops clearly. Commuters just know. The water is not clean, there's a technique to pulling up the plastic sheeting along the sides to avoid getting splashed when another boat passes, and nobody's pretending it's a romantic experience. But it moves sixty thousand people a day through a city with some of the worst road traffic on the planet.
The experience is more "I'm commuting in a floating bus and might get canal water on my shoes" than "I'm gliding past temples in a teak boat." I appreciate the honesty of that. What's the pollution comparison there? A longtail boat with a diesel engine versus sitting in a bus stuck in Bangkok traffic for an hour?
Let's get into the emissions comparison, because this is really the heart of Daniel's question. When you compare a bus to a fuel-efficient motorized boat, you have to look at a few things. First, fuel type. Second, engine load and efficiency. Third, passenger capacity. A modern diesel city bus gets roughly three to five miles per gallon and carries about fifty to eighty passengers. A typical water taxi or canal boat with a similar diesel engine is going to get worse fuel economy per mile, because pushing through water creates more resistance than rolling on asphalt.
Water is denser than air. Boats are always fighting drag in a way that wheeled vehicles aren't.
The drag coefficient in water is about eight hundred times higher than in air. So even if you have a fuel-efficient marine diesel, you're burning more fuel to move the same mass over the same distance compared to a bus on a road. But — and this is where the comparison gets interesting — the operational environment changes everything.
Because the bus is sitting in traffic.
The bus is sitting in traffic. A diesel bus in Bangkok stop-and-go traffic is operating at its least efficient. Idling, accelerating, braking, idling again. The engine rarely reaches optimal operating temperature or load. A canal boat on an unobstructed waterway is running at a steady speed with relatively constant engine load. Marine diesels are designed for exactly that — sustained operation at a specific RPM range. So the per-passenger-per-mile fuel efficiency gap narrows considerably when you compare real-world conditions rather than ideal test-track numbers.
The theoretical advantage of the bus gets eaten by the reality of urban congestion. What about the actual pollutants? Because Daniel's original data was about nitric oxide in Jerusalem. Different engines, different emissions profiles.
This is where marine engines have historically been terrible. Marine diesel has traditionally been much dirtier than road diesel. Until recently, international shipping used bunker fuel with sulfur content up to three and a half percent — compared to road diesel which is capped at about ten to fifteen parts per million in most developed countries. That's orders of magnitude difference in sulfur oxide emissions.
A cargo ship burning bunker fuel is a floating environmental disaster, but we're not talking about cargo ships. We're talking about small passenger boats. What are they running?
It varies enormously. In Venice, there's been a significant push toward electrification and hybrid systems. The city has been offering incentives for electric boat conversions, and the water bus system — the vaporetto — has been transitioning to hybrid and electric models. But many of the smaller delivery boats and water taxis are still running conventional diesel. In Bangkok, the canal boats are almost entirely diesel, and they're not necessarily modern, clean-burning engines. The air quality along the khlongs is not great.
If we're doing an honest comparison, a diesel canal boat versus a diesel bus: the boat probably produces more CO2 per passenger-mile in ideal conditions, but in real city conditions the gap is smaller. And on other pollutants — particulate matter, nitrogen oxides — it really depends on the engine, the fuel, and whether there's any emissions control technology.
That's the fair summary. But here's what I think is the more interesting framing. When Daniel talks about Venice as a case study that "proves it can be done," he's not just talking about emissions per vehicle. He's talking about the total urban system. In Venice, the absence of cars means zero road traffic emissions in the historic center. No diesel particulates from buses, no brake dust, no tire wear particles, no resuspended road dust. All the pollution comes from boats, and it dissipates differently — it's not trapped in street canyons the way vehicle exhaust is.
That's the canyon effect we talked about in the Jerusalem context. Narrow streets trap pollutants. In Venice, the canals are open to the sky, but they're also narrow. Does the water help? Does it absorb anything?
Water doesn't absorb gaseous pollutants in any meaningful way for air quality purposes. But the air movement patterns are different. Canals create wind channels. There's usually more airflow over water than through dense urban street grids. And there's no ground-level ozone formation from the interaction of NOx and sunlight on hot pavement, because there isn't hot pavement.
The urban heat island effect must be completely different in a city with water instead of asphalt.
Venice's surface is mostly stone, water, and buildings. The thermal mass of the water moderates temperature extremes. In summer, the water absorbs heat during the day and releases it at night, but it doesn't get nearly as hot as asphalt. The surface temperature of asphalt on a summer day can hit sixty degrees Celsius — that's a hundred and forty Fahrenheit. Canal water in Venice in summer is maybe twenty-five Celsius. That temperature difference completely changes the atmospheric chemistry.
Even before we get to vehicle emissions, the urban form itself is producing different pollution dynamics. Which brings us to Daniel's broader question: what other cities have done this? Water transit as actual transit, not a tourist gimmick?
There's a spectrum. On one end, you've got cities that never abandoned their water networks. On the other, cities that have deliberately built new water transit. Let me run through a few. Kochi, in India's Kerala state. It's a network of backwaters and canals that functions as a genuine transportation system. The state water transport department runs ferry services connecting the islands and peninsulas that make up the city. About eighty thousand people use the ferries daily. These aren't tourists — they're commuters, students, market vendors.
Eighty thousand daily riders on ferries in Kochi. That's comparable to Bangkok's canal boats. What about in the developed world?
Rotterdam is an interesting case. It's a modern city with extensive roads, but it also has a water taxi network that's integrated into the public transit system. The water taxis are speedboats, basically — they carry eight to twelve passengers and operate on demand. You can book them through an app. They're not cheap, but they're faster than ground transport for certain routes because they bypass road congestion entirely. Rotterdam also has a water bus system for higher-capacity routes.
An app-based water taxi. That's the Uber of boats.
That's essentially what it is. And it works because Rotterdam's geography demands it. The city is built around the Nieuwe Maas river, and some destinations that are very close as the crow flies require a long detour by bridge or tunnel. The water taxi takes a direct line. It's not a replacement for the road network — it's a complement that exploits the specific geometry of the city.
Which might be the smarter way to think about this. Not "can we replace roads with canals," but "where do waterways already exist, and how can we use them to take pressure off the road network?
And that's the model in a lot of places. Sydney's ferries carry about fifteen million passengers a year across the harbor. Brisbane has a CityCat ferry system that's been running since the nineties and carries about six million passengers annually. Both are integrated with the broader transit card system — same ticket, same fare structure. They're not niche alternatives, they're core transit infrastructure.
In both cases, the geography makes it obvious. Sydney Harbour is this massive natural feature that cuts through the city. Driving around it takes forever. A ferry straight across is fifteen minutes. The mode choice isn't ideological — it's just the smartest way to move people.
And that brings me to a city that's doing something genuinely new: Amsterdam. Which sounds obvious — Amsterdam has canals. But the canals in Amsterdam have historically been more decorative and recreational than functional for transit. That's changing. The city has been developing water-based logistics to reduce truck traffic in the historic center. There's a fully electric cargo vessel called the City Supplier that delivers goods to businesses along the canals, replacing diesel truck deliveries. It's a pilot program, but the results have been promising enough that they're expanding it.
An electric cargo boat replacing delivery trucks in Amsterdam. That's directly relevant to Daniel's Amazon-in-Venice observation. What's the capacity on something like that?
The City Supplier can carry about four tons of cargo, which replaces roughly four to five delivery van trips per day. But the bigger impact is that it removes those vans from the narrow, crowded streets of the canal district entirely. No idling, no double-parking, no blocked bike lanes. The boats load and unload at designated quay points, and then last-mile delivery is handled by electric cargo bikes.
The boat doesn't need to dock at every business. It's a floating distribution center, and the final hundred meters is bikes. That's clever infrastructure design. It's not boat versus truck — it's boat plus bike versus truck.
That's the pattern that keeps showing up. Water transit works best not as a one-to-one replacement for roads, but as part of a multimodal system that exploits the advantages of each mode. Boats are efficient for moving bulk goods and groups of people along fixed water corridors. They're terrible for last-mile, door-to-door service. But neither are buses, really. You still walk from the bus stop.
Let's go back to the emissions comparison for a minute, because I think we've danced around it but haven't given Daniel the direct answer he asked for. Bus versus fuel-efficient motorized boat. Give me numbers.
A modern diesel city bus in European operation — say a Mercedes Citaro or similar — emits roughly one thousand to one thousand two hundred grams of CO2 per kilometer. With an average occupancy of about twenty passengers, that's roughly fifty to sixty grams of CO2 per passenger-kilometer. A high-occupancy bus at rush hour with fifty passengers drops that to about twenty to twenty-five grams per passenger-kilometer.
Depends heavily on the boat. A diesel water bus like the vaporetto in Venice, carrying about two hundred passengers, is going to emit somewhere around one hundred fifty to two hundred grams of CO2 per passenger-kilometer. So three to four times worse than a half-full city bus on a CO2-per-passenger basis. A smaller water taxi with a diesel engine carrying eight passengers might be three hundred grams or more per passenger-kilometer.
On pure CO2, the bus wins, sometimes dramatically. But that's not the whole story, is it?
No, and this is where most coverage gets it wrong. CO2 is a global pollutant — it doesn't matter where it's emitted, it matters how much. But the pollutants Daniel was actually measuring in Jerusalem — nitric oxide, nitrogen dioxide, particulate matter — those are local pollutants. Their health impact depends entirely on where they're emitted. A boat emitting NOx in the middle of a waterway with good air circulation is not the same as a bus emitting NOx in a street canyon where people are walking and living in the breathing zone.
The boat's emissions disperse over open water. The bus's emissions accumulate between buildings.
There's another factor that almost nobody discusses: non-exhaust emissions. Brake wear, tire wear, and road dust resuspension account for a significant fraction of particulate matter from road vehicles — in some studies, more than the tailpipe emissions for modern vehicles with good particulate filters. Brake wear alone can contribute twenty to thirty percent of traffic-related PM10 in urban areas. Boats don't have brakes in the same way — they reverse thrust or use water resistance to slow down, which produces no particulate emissions. And they don't wear down tires on pavement.
The tailpipe comparison might favor the bus, but the total particulate picture is more complicated. What about noise? Daniel mentioned noise pollution specifically.
Noise is where boats have a genuine structural advantage. A diesel bus accelerating from a stop produces about eighty to eighty-five decibels at close range. A marine diesel running at constant speed on a boat is quieter — not silent, but typically sixty-five to seventy-five decibels, and the sound propagates differently over water. It doesn't echo off buildings the way street noise does. But the bigger factor is that boat noise is steady-state, not the constant stop-start, acceleration-deceleration pattern that makes urban traffic noise so intrusive.
Daniel mentioned the honking in Jerusalem specifically. Boat captains are not sitting in traffic leaning on their horns.
They're really not. And there's research on this — steady-state noise at moderate levels is less physiologically stressful than intermittent, unpredictable noise at the same average decibel level. Your brain habituates to a constant hum. It can't habituate to random honking and engine revving. So even at equivalent sound pressure levels, the boat traffic is likely to be less annoying and less health-impacting than road traffic.
That's a non-obvious insight. The same decibels don't mean the same stress response. Alright, let's broaden out. Daniel asked about places where waterways are in serious use. We've covered Venice, Bangkok, Kochi, Rotterdam, Sydney, Brisbane, Amsterdam. What else belongs on this list?
I want to mention two more because they're very different models. The first is Tokyo. People don't think of Tokyo as a water city, but it has an extensive network of rivers and canals, and the water bus system — the Tokyo Mizube Line — connects several districts including Asakusa, Odaiba, and Hamarikyu. It's not a primary transit mode for most commuters, but it carries significant passenger volumes and it's integrated into the tourism and leisure infrastructure in a way that takes pressure off the rail system during peak tourist periods.
It's not daily commute for most people, but it's real transportation infrastructure.
The second is a much more niche example: the backwater taxi system in Alappuzha, Kerala. This is the Kerala backwaters, which are a network of brackish lagoons and canals parallel to the Arabian Sea coast. For the local population, these waterways have been the primary transportation network for centuries. Kids go to school by boat. Farmers move produce by boat. There's a government-run ferry system that connects dozens of villages. It's not a city system in the Venice sense, but it's a functioning water transit network that serves a dispersed rural and semi-urban population.
That's a reminder that water transit isn't just for dense historic city centers. It's also the most practical option when the geography is water-logged and building roads is expensive or impossible.
Building a road through a wetland or a delta region requires drainage, embankments, bridges — it's enormously expensive and environmentally destructive. Maintaining a canal network is not trivial either, but in many of these places the canals already exist, have existed for centuries, and the alternative isn't a nice paved road, it's no transportation infrastructure at all.
Which brings up a question I haven't heard discussed much. We've been comparing boats to buses as if the choice is between two existing systems. But what about the embedded carbon of the infrastructure itself? Building a road versus maintaining a canal.
That's a fascinating comparison and I wish there were better lifecycle analysis data on it. A canal requires dredging, bank reinforcement, lock maintenance if there's elevation change, and water management. A road requires aggregate, asphalt or concrete, ongoing resurfacing, drainage systems, and snow removal in colder climates. My instinct is that canals have lower embedded carbon per ton-kilometer of freight moved, but I'm not confident in that without better data.
Let's talk about the future, then. If we're looking at water transit not as a historical curiosity but as a growing mode, what's happening with electrification?
This is moving fast. Electric ferries are already operational in several places. Norway has been leading on this — the ferry Ampere has been operating since twenty fifteen as a fully electric car and passenger ferry. It crosses the Sognefjord, about six kilometers each way, and it charges at both terminals from batteries that are topped up during the short turnaround time. The operational cost savings are enormous — about eighty percent reduction in fuel costs and significant maintenance savings because electric motors have far fewer moving parts than marine diesels.
Eighty percent fuel cost reduction. That's the kind of number that makes transit agencies pay attention, regardless of environmental considerations.
That's Norway in twenty fifteen. The technology has improved significantly since then. Battery energy density is up, costs are down. There are now fully electric water taxis operating in several cities. Stockholm has electric ferries. Copenhagen has an electric harbor bus. Even Venice has been testing electric vaporettos, though the transition is slow because the existing fleet is large and the investment is significant.
The charging infrastructure must be the bottleneck. You can't exactly pull a ferry over to a charging station.
The solution that's emerged is high-power charging at docks during the normal passenger loading and unloading cycle. The Ampere ferry charges with a ten-minute burst at each terminal. That requires serious electrical infrastructure — we're talking megawatt-level charging. But for fixed-route ferry services, the predictability of the route and schedule makes it feasible. It's much harder for on-demand water taxis that might go anywhere.
The ferry routes are the low-hanging fruit. Fixed route, fixed schedule, known energy requirements, charging at both ends. That's a solvable engineering problem. The water taxi equivalent of an Uber is much harder to electrify.
Though it's coming. There are companies working on this — Candela in Sweden has developed an electric hydrofoil boat that reduces energy consumption by about eighty percent compared to a conventional planing hull. It lifts out of the water on foils, which dramatically reduces drag. They've been testing them as water taxis in Stockholm, and the energy consumption is low enough that the battery range is actually practical.
A hydrofoil water taxi. I'm trying to picture Daniel hailing one of those in Jerusalem. Not going to happen, but the technology is interesting. How does the hydrofoil affect wake and noise?
Significantly reduced wake, which matters in cities like Venice where wake damage to building foundations is a serious concern. The foil boats produce almost no wake at operating speed because the hull isn't pushing through the water. And the noise is dramatically lower — it's basically the hum of an electric motor plus the sound of water against the foils, which is minimal compared to a marine diesel.
If we're projecting forward, the emissions comparison between an electric bus and an electric ferry or electric water taxi starts to look very different from the diesel comparison. Both are zero tailpipe. The ferry might actually have lower per-passenger energy consumption in some cases because of the steady-speed operation versus stop-start urban driving.
That's the thing about electrification — it resets the efficiency comparison. An electric motor is about ninety percent efficient at converting stored energy to motion. A diesel engine is about forty to forty-five percent efficient at best, and much worse in urban stop-start conditions. So even if the boat is pushing through water, which requires more energy than rolling on asphalt, the efficiency gain from the electric drivetrain partially offsets that.
Which means the future of water transit looks a lot cleaner than the present. But we're not in the future yet. For someone like Daniel, living in a city that doesn't have canals and isn't going to dig them, what's the actionable takeaway from all this?
I think the actionable takeaway is about mode diversity. The cities that handle transportation best are not the ones that picked the single best mode and went all-in on it. They're the ones that have multiple overlapping networks — walking, cycling, buses, trains, ferries where geography allows — and let people choose the best mode for each trip. Water transit is never going to be the backbone of urban transportation in most cities because most cities aren't built on navigable water. But where the water exists, using it for transit is almost always under-exploited.
The pollution lesson from Venice isn't "boats are cleaner than buses." It's "getting cars out of city centers produces air quality benefits that are immediate and measurable." Whether you replace them with boats, bikes, trams, or just pedestrianization, the removal of combustion engines from dense urban street canyons is what matters.
The mode that replaces the car matters less than the fact that the car is gone. And Daniel's Shabbat data from Jerusalem is a perfect natural experiment demonstrating exactly that. When the cars stop, the air cleans up.
Now: Hilbert's daily fun fact.
A single honeybee produces about one-twelfth of a teaspoon of honey in its entire lifetime.
For listeners who want to think practically about this: if you live in a city with waterways, pay attention to whether they're being used for transit. Support ferry service expansions, water taxi pilot programs, and cargo boat trials. The infrastructure is already there — the water is right there. Using it is often cheaper than building new roads or rail lines. If you don't live in a water city, the lesson is about mode diversity more broadly. The best transportation system is the one that gives people options, and every option that takes a combustion engine out of a street canyon is a win for local air quality.
If you're just curious about this stuff as an urban design question, Venice is the place to visit — but not just the tourist Venice. Go to the Cannaregio district in the morning and watch the delivery boats. Watch the garbage collection. Watch the ambulance speedboat dock at the hospital. It's a living city that happens to float, and it's been making car-free urbanism work for a thousand years. There's a lot to learn from it.
The other thing I'd say is that the electrification of water transit is happening faster than most people realize. If you're a city planner or a transit advocate, the technology is ready. The Norwegian ferry example from twenty fifteen has been replicated and improved. Electric water taxis exist. Electric cargo boats exist. The barriers are regulatory and financial, not technical.
One last point on the emissions question, because I want to make sure we didn't leave this fuzzy. In the current world, with current technology, a diesel bus is generally cleaner per passenger-kilometer than a diesel boat. But that comparison is misleading in two ways. First, the boat's emissions are emitted in a less harmful location — open water rather than street level. Second, the comparison is between a mature technology with decades of emissions regulation and a much less regulated sector. Marine engines are catching up fast on emissions standards, and electrification will leapfrog the whole debate.
The honest answer is: it depends. On the engine, the fuel, the passenger load, the route, the alternatives. But the direction of travel is clear, and water transit is going to get cleaner faster than road transit because it's starting from a dirtier baseline and the electrification economics are compelling.
Thanks to our producer Hilbert Flumingtop for keeping this show running, and to Daniel for a prompt that sent us down a interesting rabbit hole. This has been My Weird Prompts. You can find every episode at myweirdprompts.
Until next time.
