The engineering approach
|The engineering approach to intersection design: traffic flows are an input that once determined is never modified|
The economic/behavioral approach
|Example of mode comparison for one trip, all modes except walking makes the trip worth it, though using a car is most expensive, as it saves time, it has the highest benefit/cost ratio|
Now, of course people don't bother making these calculations to the cent, but they do some estimates in their minds on some level. Everyone is different, and if you summed up everyone's thresholds together, you would obtain something like a demand curve:
Visually, the process becomes much more complicated with more feedback loops:
|Engineering process revised to include an economic approach to congestion|
Some ideas of an economic approach to congestion
- Spatial and temporal redistribution of trips: in that case, certain trips are delayed or hastened, or go through alternative roads that are less congested. When the costs of congested paths during peak hours become relatively higher than alternatives, then people are less likely to opt for them. This is most effective for elective trips without a fixed schedule or when alternative paths exist, which is not always the case (ex: bridges).
- Elimination of trips: when costs of trips increase, the cost may become higher even than the expected individual benefit of the trip, in which case, the trip can be canceled. In this case, what brings about the change is not relative cost, but the absolute cost of the trip that gets too high for it. This may be a problem for the local economy, but it may also favor the replacement of regional trips by local trips, which may be good for local communities. Commutes are least sensitive to that possibility, because benefits tend to be very high, and during congested times, commutes tend to be the majority of trips, so the ability of this approach of reducing congestion during peak hours is small.
- Favoring travel modes that are more space-efficient: walking, biking and transit all use a lot less space than single-occupancy vehicle. For example, a simple bus line with 12 trips per hour (1 per 5 minutes) can increase passenger throughput by 70% (700 people per hour versus 1 000 people per hour for a regular street lane) while using only 1% of that lane's hourly vehicle capacity. In this case too, the effect comes from relative cost, not absolute cost.
I will provide a few examples of different practical ways of achieving this, ideally based on real-life examples. But first, I want to address something. The idea of regulating or influencing individual behavior through policies based on economics often leads to accusations of social engineering. I just want to respond that neutrality in this case is essentially impossible. Streets and roads, by their very design, are public goods except for a few exceptions, as such, funding for them is determined by the public authority responsible for them. Therefore, that public authority is forced to make a choice, and the choice it makes will necessarily affect users' behavior and consumption of that good.
Letting congestion take care of it
The biggest problem is that roads do have a major economic role to play in the modern world, for freight and for rapid movement of public and private services. Congestion is much worse for these vehicles than for commuters, because they delay the provision of services and may slow certain economic activities. Congestion can also be disastrous for transit, the alternative mode that is best placed to replace SOV trips during congested commute periods as high demand periods result in higher frequencies (making transit best in peak hours and worse in off-peak periods, the opposite of private vehicles). The slower transit vehicles go, the more expensive they are to run, so if transit runs in mixed traffic, congestion can be disastrous for it. That is what killed the streetcars.
Finally, in terms of development incentives, congestion can lead to sprawl as industries and other developments flee congested areas. Since congestion is rare outside of peak hours, commercial developments are much less affected by it, so having congested arterials do nothing to keep commercial areas in the heart of residential developments.
So, to sum up, developing a greater tolerance for congestion is not bad, but relying exclusively on congestion to regulate traffic is a bad approach.
|Schematic example of a congestion charge system, every vehicle crossing the dotted red line gets charged a certain amount|
|The Easy Solution to Congestion... I'm only partly facetious, it's politically suicidal, but it would work|
|A theoretical congestion charge zone for Montréal, relatively easy to do thanks to the location of the city on an island...|
|...but in Toronto, it would be extremely complicated to apply because there is no obvious boundary and any border would cut through a lot of streets, including small side streets|
Tolling high-speed roadways
For example, here is a theoretical comparison between 5 trip choices, supposing a time value of 20$ per hour:
- A commute from a suburb 20 km away on an highway, without toll
- A 10-km commute from an inner suburb on lower-speed roads
- The first 20 km commute but with a 10 cents/km cost added
- A 10-km bus commute with a monthly pass (so no marginal cost)
- A 20-km bus commute with a monthly pass also
|Comparison of different scenarios|
Once you add a toll to the highway, the 10-km car commute becomes the cheapest option. The actual monetary cost (excluding time) is also 3 times higher than with the car commute, so that the annual cost, just in variable costs, is about 1 500$ higher for the 20-km highway commuter over the 10-km urban car commuter. That is not a negligible difference.
A great thing with this approach over the congestion charge approach is that tolling highways increases the cost of ALL long distance trips, and not just trips to the city core. So people can't simply escape the fees by moving to suburbs and finding jobs in other suburbs.
|With a congested central city and/or a congestion charge, developments (homes AND jobs) tend to flee to suburbs to avoid the congestion in the center, favoring inter-suburb trips|
|With tolled highways, inter-suburb trips are just as expensive as working downtown, so developments tend to gather in nodes to reduce distances, thus reducing or eliminating the need to use highways for many residents|
Building low-cost, high-capacity, low-speed road networks
Examples of this approach can be found in Japanese and European cities, where high-speed roadways skirt around urban areas, but with a high number of major streets in cities that have low speed limits.
|Munich, Germany, the highways are in orange, see how they circle the city but do not enter it, average speed on urban arterials without congestion, according to Google Maps, is about 25-30 km/h, 15 to 20 mph|
|Sendai in Japan, another example of highways avoiding the urban area, but with a strong grid of arterials inside the city, according to Google Maps, without congestion, the average car speed on these arterials is 25 km/h, 15 mph|
The problem of this approach is a risk of the creation of a semi-independent edge city around the highways that skirt the town if no measure (toll, planning) is taken to prevent it, which will eventually congest that peripheral highway, complicating long-distance trips and road freight much.
Now, I know what some may say: this is all fine and good, but that option seems to be valid only if we start from scratch what if we already have a hierarchical road network with plenty of highways inside our metro areas?
The answer is that you can gradually transfer over to that system by converting highways to boulevards like some cities did, and applying traffic-calming measures on major arterials to slow traffic down.
Limiting parking or increasing parking costs
As far as examples go, Calgary is an example of a city that let downtown parking prices rise very high. The average downtown parking spot going at over 450$ per month, which is very high for a city with just over 1 million people. Ottawa is an example of maximum parking limits, especially downtown. The result of Ottawa's policy is a very high transit use by downtown commuters, that some credit to Ottawa's BRT... except that the high transit use was present long before the BRT, which opening is not associated with any increase in transit use.
The same can go for residential parking, which is even more crucial, because if people do not have a place to park their car at home, they can't even own one, and if they can't own one, they can't use a car to get around, at least not regularly. The presence of on-street parking can short-circuit this process as people may simply park on the street without having to pay for a spot, which is why residential parking permits make a lot of sense.
On a tangent, many cities currently limit population and job densities in areas to keep vehicle traffic at a manageable levels. Except that is based on the supposition that, no matter what. people are going to travel by cars, or maybe that being able to own a car and to use it is a basic right. In fact, people have different ways of getting around, and those without cars are even forced to find other ways of getting around. So if you want to limit vehicle trips to avoid congesting the road network, instead of restricting population/job density, why not restrict vehicle density by restricting the number of parking spots available? That way, you can restrict vehicle trips without actually restricting development unduly.
Anyway, limiting parking or having higher parking fees is a bit like a congestion charge as in they mainly target people who go downtown or any dense areas, because in lower density areas, parking is likely to be more abundant and affordable, if not outright free.
Invest in rapid transitIf you look at the economic comparison between modes above, you can notice that regular local buses do very poorly in the comparison, even compared to commutes twice as far on tolled highways. To make transit more attractive, you can try to reduce the cost of tickets, but that is not why transit is not used that much in general. With monthly passes, the marginal cost of transit use is even 0$, so it's hard to see how you could do better by subsidizing transit more. The issue is the cost of transit use in time, so to attract people to transit, it's best to have rapid transit.
|Rapid transit makes transit competitive in terms of marginal cost, which local buses generally fail to do|