SEPTA has recently had difficulty providing sufficient train capacity on the Market-Frankford Line (MFL), the busiest on its network. It has rebuilt some cars, reducing the number of seats to increase standing capacity. However, it has also downgraded the line from skip-stop — with two A/B trains, each of which made different stops along the line — to all-stop during travel peaks. That decision is a serious mistake that should be corrected by returning to accelerated skip-stop service.

Skip-stop service is not as fast as express on four-track sections on the Broad Street Line. However, skip-stop is the only way to provide service significantly faster than all-stop on a two-track line. Although skip-stop lengthens headways (intervals between trains) at A and B stations, it provides higher average speed of all trains.

Higher speed on transit lines — trains and buses — is extremely important because it attracts more passengers and reduces the number of trains required for any given headway. Attracting more passengers and reducing operating costs benefits the public and SEPTA.

Since each train in skip-stop service has to make fewer stops than an all-stop train, its cycle (roundtrip) time is significantly shorter. That decreases the number of trains needed to provide a given headway. Thus, all-stop service on MFL takes longer travel times.

All-stop service may be simpler to control, but it results in lower average speed, not greater line capacity. Even though SEPTA insists they can use the same amount, in reality, the change requires more trains to maintain service. This conclusion is supported by a comparison of skip-stop vs. all-stop transit operation, using the MLF as an example, which my research team at the University of Pennsylvania published in 1976. We found that the MFL’s skip-stop trains, which then served six A/B station pairs, made a trip from 69th Street to the Frankford Transportation Center in about six minutes less than all-stop trains. That made cycle time for each train 12 minutes shorter. It also makes sense intuitively: All-stop service offers lower operating speed because it makes more stops.

How can the capacity of MFL be increased overall? Some places to start: improving reliability of service and reducing average times between trains. Usually, the station with the longest dwell time is the critical element for line capacity. For the MFL, the 15th Street station is usually that critical element because it has the heaviest two-way passenger exchange. Commuter standing, in this case, takes very long because, at most doors, there are two standing persons, allowing only one to squeeze in or out through that narrow opening.

Several measures, such as designating stopping locations more precisely, marking door locations on the platform, using a few officers to shepherd passengers during critical periods, and having more announcements not to stand blocking the doors could help. Shortening the dwell times at critical stations increases the capacity of the entire line.

Replacing the skip-stop with less efficient all-stop service is a case where SEPTA adjusts service to make it easier for its operations, with more standardized train movement control, but less convenient for passengers. Other examples of that are found on SEPTA’s Regional Rail System: its lines have mostly irregular and very long headways, and their clearly designated R-1, R-2, etc., have been replaced by random mixing of unnumbered lines between the east and west lines, converging to Center City Tunnel. Signs on the trains are poor, often nonexistent.

On the positive side, SEPTA’s move to increase frequency of service on the MFL during evening hours is welcome for the city. Most rapid transit systems offer much shorter times between trains on their main lines than 10-15 minutes in off-peak hours and weekends. Such service makes a city more attractive and livable.

SEPTA services represent the backbone of Philadelphia and its extensive suburbs. The current countrywide revival of cities, especially their central areas, needs not only maintenance of transit services, but also their expansion and modernization. Under the leadership of the new general manager, highly experienced transportation expert Leslie Richards, SEPTA should be assisted to respond to the region’s need to become more livable in the coming years.

Vukan R. Vuchic is professor emeritus of transportation engineering and city and regional planning at the University of Pennsylvania.