Light Rail - Capacity of Light Rail Versus Roads

Capacity of Light Rail Versus Roads

One line of light rail has a theoretical capacity of up to 8 times more than one lane of freeway (not counting buses) during peak times. Roads have ultimate capacity limits that can be determined by traffic engineering. They usually experience a chaotic breakdown in flow and a dramatic drop in speed (colloquially known as a traffic jam) if they exceed about 2,000 vehicles per hour per lane (each car roughly two seconds behind another). Since most people who drive to work or on business trips do so alone, studies show that the average car occupancy on many roads carrying commuters is only about 1.2 people per car during the high-demand rush hour periods of the day. This combination of factors limits roads carrying only automobile commuters to a maximum observed capacity of about 2,400 passengers per hour per lane. The problem can be mitigated by using high-occupancy vehicle (HOV) lanes and introducing ride-sharing programs, but in most cases the solution adopted has been to add more lanes to the roads. Simple arithmetic shows that in order to carry 20,000 automobile commuters per hour per direction, a freeway must be at least 18 lanes wide.

By contrast, light rail vehicles can travel in multi-car trains carrying a theoretical ridership up to 20,000 passengers per hour in much narrower rights-of-way, not much more than two car lanes wide for a double track system. They can often be run through existing city streets and parks, or placed in the medians of roads. If run in streets, trains are usually limited by city block lengths to about four 180-passenger vehicles (720 passengers). Operating on 2-minute headways using traffic signal progression, a well-designed two-track system can handle up to 30 trains per hour per track, achieving peak rates of over 20,000 passengers per hour in each direction. More advanced systems with separate rights-of-way using moving block signalling can exceed 25,000 passengers per hour per track.

Most light rail systems in the United States are limited by demand rather than capacity (by and large, most North American LRT systems carry less than 4000 persons per hour per direction), but Boston and San Francisco light rail lines carry 9,600 and 13,100 passengers per hour per track during rush hour. Elsewhere in North America, the Calgary C-Train and Monterrey Metro have higher light rail ridership than Boston or San Francisco. Systems outside North America often have much higher passenger volumes. The Manila Light Rail Transit System is one of the highest capacity ones, having been upgraded in a series of expansions to handle 40,000 passengers per hour per direction, and having carried as many as 582,989 passengers in a single day on its Line #1. It achieves this volume by running 4-car trains of up to 1350 passengers at a frequency of up to 30 trains per hour. It is important to note, however, that the Manila light rail system has full grade separation and as a result has many of the operating characteristics of a Metro system rather than a light rail system. 1350 passengers per train is more similar to heavy rail than light rail.

A bus line using its own lanes can have a capacity of 7,000 per hour (30 buses per direction, 120 passengers in articulated buses). Bus traffic is the traditional alternative to light rail, at least if very high capacity is not needed. Using buses, roads can get a high transit capacity. To have 30 buses per direction an hour, they must have priority in traffic lights and have their own lanes, as must trams to reach this density. Buses can go closer to each other than rail vehicles because of better braking capability. However, each bus vehicle requires a single driver, whereas a light rail train may have three to four cars of the same capacity in one train under the control of one driver, increasing labor costs of high- traffic BRT systems.

This chapter will handle about the capacity of a light rail and will compare it to the capacity of a car. For the light rail, the Siemens S70 is taken and for the car, a standard car with 5 seats is taken.

In Belgium and The Netherlands, engineers use ASVV (CROW, 2004) to have some standards in the transportation sector. The average length of a car is about 4.74 meter for a standard personal car (5 seats). The length of a light rail, Siemens S70, is 27.7 meters. This means that one light rail has approximately the same length as 5.8 cars.

The maximum occupancy of one car is 5 people; nevertheless the average occupancy in Belgium is only 1.8 people. The maximum capacity of the Siemens S70 is 220 persons. This means that one meter in a car is good for 1 person and one meter in a light rail is good for almost 8 persons. So the capacity of a light rail is about 8 times higher than the capacity of a car, if only the length of the vehicles is taken in consideration.

The average width of an automobile (car) is about 1.77 meters, while the average width of the Siemens S70 is about 2.7 meters. The area of a car is about 8.4 m² while the area taken up by a light rail car is about 74.8m². In a car every square meter has room for only 0.6 persons, while every square meter in a light-rail car has room for 2.9 persons. This means that a light rail is more capacity-effective than a car – a lot more. Height is not taken into consideration because it is not normally a problem given minimum-clearance regulations for underpasses.

The peak passenger capacity per lane per hour depends on which types of vehicles are allowed at the roads. If only cars are allowed, the capacity will be less and will not increase when the traffic volume increases.

When there is also a bus driving on this route, the capacity of the lane will be more and will increase when the traffic level increases. And because the capacity of a light rail is higher than the capacity of a bus, there will be even more capacity when there is a combinatCarson cars and light rail. Table 3 shows an example of peak passenger capacity.

(Edson & Tennyson, 2003)