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Light rail costs too much, does too little

The Limits of Moderate-Capacity Transit

Mar 9

2007

Gas prices in the first nine months of 2006 were at their highest levels (after adjusting for inflation) in twenty-five years. Most transit agencies made the most of this, with some gaining huge increases in ridership over the first nine months of previous year.

 

While these are exceptional, APTA reports that American transit systems carried 3 percent more transit riders than in 2005. So why did the transit system in Portland, the city that supposedly loves transit, actually carry less riders in 2006 than the year before?

Moderate-capacity transit in Portland.

The answer has to do with Portland’s choice of technology. Though light rail is often called “high-capacity transit,” in fact it is anything but. After all, the “light” in light rail refers to light loads and is a comparison with subways or elevateds, also known as heavy rail, meaning they can carry heavy loads. Light rail’s load limits have become a particular problem for Portland.

Despite claims that a light-rail line can move as many people as an eight-lane freeway, light rail’s capacity is in some cases less than a single freeway lane. A system’s capacity to move people depends on vehicle frequencies or headways, the number of occupants per vehicle, and vehicle speeds.

Freeway lanes can move about 1,800 cars per hour at speed, or one every two seconds. Exclusive bus lanes can move about 360 buses per hour, or one every ten seconds. Rail frequencies are much lower and depend on the quality of signaling. Typically, light-rail systems allow no more than one train every three minues, while some heavy-rail systems may allow one train every two minutes.

Many rail advocates compare rail capacities with average auto occupancies, but this is apples to oranges. Auto capacities depend on the size of auto, but let’s assume an average of five. Bus capacities are typically about 80 people including standees.

Train capacities depend on the number of cars per train. Heavy rail runs exclusively on its own rights of way, so the number of cars is limited by the length of station platforms. Most heavy-rail lines are built for trains of eight cars. Subway cars can carry about 180 people, so a train can carry more than 1,400 people.

In contrast, most light-rail trains spend at least part of their time on city streets. To avoid blocking traffic, this means that train length is limited by the shortest blocks where a train might stop. Downtown Portland has unusually small blocks — only 200 feet on a side — and because light-rail cars are about 90-feet long, Portland can run no more than two cars at once. Many other light-rail cities have three-car trains, but only a few run more than three cars per train..

The capacity of a light-rail car is about 170 people, so Portland trains can carry no more than 340 people. All these transit capacities, by the way, are “crush capacities,” meaning Tokyo-like crowding rarely seen in the U.S. I rode a very crowded DC subway today and counted 80 seated and 50 standing, about 50 short of the crush capacity.

Many rail advocates ignore speed, but speed is an important component of the amount of work a transportation system does. On the 50th anniversery of the Golden Gate Bridge, the bridge was briefly closed to autos and opened excusively to pedestrians. More people walked across the bridge in one hour than had ever driven across it in that amount of time. But no one thinks the bridge would do more work if it were closed to autos because autos are so much faster than walking.

Light-rail trains average about 22 mph. Some heavy-rail lines average 40 mph. Most urban freeways can handle cars or buses at 65 mph.

Multiply these numbers out and we get the following capacities in passenger miles per hour:

Even a four-car light-rail line could do less work than a freeway lane open to autos. A freeway lane open only to buses could do a little more work than a heavy-rail line and more than eight times as much work as a three-car light-rail line. Even if bus-lane speeds averaged only 10 mph (as on normal city arterials), the bus lane could do far more work than any light-rail line.

All of these numbers, of course, are far more than actual use. In 2005, the average auto had 1.6 people; the average transit bus carried 10.3 people; the average light-rail car carried 25.5 people; and the average heavy-rail car carried 22.9 people. Based on these numbers, typical hourly flows are shown in the table below.

Once again, the bus lanes beat even heavy rail and carry seven times as many people as three-car light rail. Buses have another advantage: individual buses can easily serve numerous neighborhoods or districts, then get on the bus lanes and head for downtown or other major centers. By comparison, rail cars tend to empty out as they near urban fringes. That means the buses can carry more people over a longer portion of their routes than rail lines.

Actual use is more realistic than capacity, but sometimes capacity is important. Portland’s light-rail system is more successful than most, but this very success works against it because of the system’s limited capacity.

In deciding to build light rail, Portland selected the wrong technology for a city with short blocks. Even a city with long blocks would do better by building virtual exclusive bus lanes — bus lanes open to toll-paying cars with tolls set to prevent any congestion — rather than light rail.

Now Portland is making matters even worse by tearing up its bus mall to add a new light-rail line to it. The bus mall is already near to its capacity for moving people. But adding light rail will actually reduce the route’s capacity for moving people.

Tearing up the bus mall to install light rail. Photo courtesy of PDX Pete.

Why not put the light rail on some street parallel to the bus mall? Because downtown businesses all agreed that, while they wanted light rail, they did not want it on their streets. Construction of the bus mall in the 1970s put many stores out of business, and retailers and restaurants on other streets did not want the same to happen to them. Since most of the businesses were already gone from the bus mall, that was the only place to build.

So don’t expect Portland transit ridership to grow much any time soon. Just remember that in Portland, reality doesn’t matter; image does.

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Reprinted from The Antiplanner

 

2-car LRT           149,600

3-car LRT           244,400

8-car HRT        1,728,000

Freeway lane      585,000

Bus lane         1,872,000

2-car LRT             22,176

3-car LRT             33,274

8-car HRT           219,840

Freeway lane      187,200

Bus lane            241,020