Worsening traffic requires new solutions
As our population increases, the traffic congestion in cities continues to worsen. In the Bay Area my commute into the city now takes about 20% longer than it did 10 years ago, and driving outside of typical rush hours is now often a major problem. In New York, the subway system helps quite a bit, but most of Manhattan is gridlocked for much of the day.
The two key ways of relieving cities from traffic snarl are:
- Reduce the number of vehicles on city streets
- Increase the speed at which vehicles move through city streets
Metro areas have been experimenting with different measures to improve car speed, such as:
- Encouraging carpooling and implementing high occupancy vehicle lanes on arteries that lead to urban centers
- Converting more streets to one-way with longer periods of green lights
- Prohibiting turns onto many streets as turning cars often cause congestion
No matter what a city does, traffic will continue to get worse unless compelling and effective urban transportation systems are created and/or enhanced. With that in mind, this post will review current alternatives and discuss various ways of attacking this problem.
Ride sharing services have increased congestion
Uber and Lyft have not helped relieve congestion. They have probably even led to increasing it, as so many rideshare vehicles are cruising the streets while awaiting their next ride. While the escalation of ridesharing services like Uber and Lyft may have reduced the number of people who commute using their own car to work, they have merely substituted an Uber driver for a personal driver. Commuters parked their cars when arriving at work while ridesharing drivers continue to cruise after dropping off a passenger, so the real benefit here has been in reducing demand for parking, not improving traffic congestion.
A simple way to think about this is that the total cars on the street at any point in time consists of those with someone going to a destination plus those cruising awaiting picking up a passenger. Uber does not reduce the number of people going to a destination by car (and probably increases it as some Uber riders would have taken public transportation if not for Uber).
The use of optimal traffic-aware routing GPS apps like Waze doesn’t reduce traffic but spreads it more evenly among alternate routes, therefore providing a modest increase in the speed that vehicles move through city streets. The thought that automating these vehicles will relieve pressure is unrealistic, as automated vehicles will still be subject to the same movement as those with drivers (who use Waze). Automating ridesharing cars can modestly reduce the number of cruising vehicles, as Uber and Lyft can optimize the number that remain in cruise mode. However, this will not reduce the number of cars transporting someone to a destination. So, it is clear to me that ridesharing services increase rather than reduce the number of vehicles on city streets and will continue to do so even when they are driverless.
Metro rail systems effectively reduce traffic but are expensive and can take decades to implement
Realistically, improving traffic flow requires cities to enhance their urban transport system, thereby reducing the number of vehicles on their streets. There are several historic alternatives but the only one that can move significant numbers of passengers from point A to point B without impacting other traffic is a rail system. However, construction of a rail system is costly, highly disruptive, and can take decades to go from concept to completion. For example, the New York City Second Avenue Line was tentatively approved in 1919. It is educational to read the history of reasons for delays, but the actual project didn’t begin until 2005 despite many millions of dollars being spent on planning, well before that date. The first construction commenced in April 2007. The first phase of the construction cost $4.5 billion and included 3 stations and 2 miles of tunnels. This phase was complete, and the line opened in January 2017. By May daily ridership was approximately 176,000 passengers. A second phase is projected to cost an additional $6 billion, add 1.5 more miles to the line and be completed 10-12 years from now (assuming no delays). Phase 1 and 2 together from actual start to hopeful finish will be over two decades from the 2005 start date…and about a century from when the line was first considered!
Dedicated bus rapid transit, less costly and less effective
Most urban transportation networks include bus lines through city streets. While buses do reduce the number of vehicles on the roads, they have several challenges that keep them from being the most efficient method of urban transport:
- They need to stop at traffic lights, slowing down passenger movement
- When they stop to let one passenger on or off, all other passengers are delayed
- They are very large and often cause other street traffic to be forced to slow down
One way of improving bus efficiency is a Dedicated Bus Rapid Transit System (BRT). Such a system creates a dedicated corridor for buses to use. A key to increasing the number of passengers such a system can transport is to remove them from normal traffic (thus the dedicated lanes) and to reduce or eliminate the need to stop for traffic lights by either altering the timing to automatically accommodate minimal stoppage of the buses or by creating overpasses and/or underpasses. If traffic lights are altered, the bus doesn’t stop for a traffic light but that can mean cross traffic stops longer, thus increasing cross traffic congestion. Elimination of interference using underpasses and/or overpasses at each intersection can be quite costly given the substantial size of buses. San Francisco has adopted the first, less optimal, less costly, approach along a two-mile corridor of Van Ness Avenue. The cost will still be over $200 million (excluding new buses) and it is expected to increase ridership from about 16,000 passengers per day to as much as 22,000 (which I’m estimating translates to 2,000-3,000 passengers per hour in each direction during peak hours). Given the increased time cross traffic will need to wait, it isn’t clear how much actual benefit will occur.
Will Automated Car Rapid Transit (ACRT) be the most cost effective solution?
I recently met with a company that expects to create a new alternative using very small automated car rapid transit (ACRT) that costs a fraction of and has more than double the capacity of a BRT. The basic concept is to create a corridor similar to that of a BRT, utilizing underpasses under some streets and bridges over other streets. Therefore, cross traffic would not be affected by longer traffic light stoppages. Since the size of an underpass (tunnel) to accommodate a very small car is a fraction of that of a very large bus, so is the cost. The cars would be specially designed driverless automated cars that have no trunk, no back seats and hold one or two passengers. The same 3.5 to 4.0-meter-wide lane needed for a BRT would be sufficient for more than two lanes of such cars. Since the cars would be autonomous, speed and distance between cars could be controlled so that all cars in the corridor move at 30 miles per hour unless they exited. Since there would be overpasses and underpasses across each cross street, the cars would not stop for lights. Each vehicle would hold one or two passengers going to the same stop, so the car would not slow until it reached that destination. When it did, it would pull off the road without reducing speed until it was on the exit ramp.
The company claims that it will have the capacity to transport 10,000 passengers per hour per lane with the same setup as the Van Ness corridor if underpasses and overpasses were added. Since a capacity of 10,000 passengers per hour in each direction would provide significant excess capacity compared to likely usage, 2 lanes (3 meters in total width instead of 7-8 meters) is all that such a system would require. The reduced width would reduce construction cost while still providing excess capacity. Passengers would arrive at destinations much sooner than by bus as the autos would get there at 30 miles per hour without stopping even once. This translates to a 2-mile trip taking 4 minutes! Compare that to any experience you have had taking a bus. The speed of movement also helps make each vehicle available to many more passengers during a day. While it is still unproven, this technology appears to offer significant cost/benefit vs other alternatives.
The population expansion within urban areas will continue to drive increased traffic unless additional solutions are implemented. If it works as well in practice as it does in theory, an ACRT like the one described above offers one potential way of improving transport efficiency. However, this is only one of many potential approaches to solving the problem of increased congestion. Regardless of the technology used, this is a space where innovation must happen if cities are to remain livable. While investment in underground rail is also a potential way of mitigating the problem, it will remain an extremely costly alternative unless innovation occurs in that domain.