Scheduling 104: Headways and Span of Service

Welcome to Scheduling 104

Today's discussion will focus on how a line's headway and span of service factor into the making of a schedule. As previously mentioned, a schedule is made up of trips with times given at certain points of a line where a bus is due to arrive.

The time between those trips is called a headway. The official MTA definition is the "time interval between vehicles moving in the same direction on a particular route, also known as frequency."

Each "link" has a set policy of headways. The CityLink service is scheduled to operate from as little as every nine minutes to fifteen minutes during the rush hours, ten to twenty minutes during the day, and twenty to sixty minutes into the evening and late night. The LocalLink service varies from every 10 minutes to 70 minutes, depending on the line. And the Express BusLink, which operates during rush hours mimic the CityLink headways, depending on the corridor it covers.

Looking at the CityLink Gold schedule, in the morning, it runs from as little as eight minutes to as much as every hour. During the rush hour, the main part of the route, called the trunk (that'll be discussed later) is scheduled to operate every 12 minutes between Walbrook Junction and North & Wolfe Street (though the timetable shows North & Greenmount as the last trunk timepoint) However, beyond that point, the line goes into two directions, one continues on North Avenue to Patterson Park & Lanvale, also known as Berea, and the other heads south to Canton Crossing. So each branch operate every 24 minutes or so. In the midday, it is still every 12 minutes, however, the Canton Crossing is reduced to every 3rd trip or every 36 minutes from Walbrook Junction, and the Berea trips are doubled. 

  

Ridership also determines the amount of trips on a line and its headway. For example, the 65, considered the "Amazon Shuttle" operates multiple trips during their shift times, which is both within and outside of rush hours. The headway varies but generally is every 10-15 minutes during shift times and hourly outside of them because the line doesn't generate high ridership otherwise. 

 

Another factor that goes into determining headways is whether the line connects to major transfer centers, like a Metro Station or Light Rail Station, equally heavy routes, and serves a large portion of the city. Those CityLink and localLink lines are labelled under the Frequent Transit Network, which has headways generally 15 minutes or less between 6am-7pm. 

The 22 is one such line. It connects to a Metro Station (Mondawmin) and crosses multiple lines between Mondawmin and Hopkins Bayview. The headway reflects how busy the line is during the day:

In the three schedules posted, they all have different start and end times. This is called Span of Service. It is "a period of time a route is in operation, measured from the time the first trip in either direction begins until the last trip in either direction ends." 

The CityLink Gold is considered a 24-hour route as the first trip begins at 3:07am and the last trip ends at 3:08am

Span of service varies depending on the route and the area it serves. The 57, known as the Belair-Edison Shuttle, operates from 6am-7pm because the area it serves, a residential community, uses the bus during that time and after 7pm, the shopping centers are closing down for the night.

 Then you have a line like the 75, which generally shuttle workers to/from BWI Airport, Amazon, and Arundel Mills. Because workers at those location, as well as others, need to be there at a certain time, and the Light Rail isn't operating overnight, the 75 has become a 24-hour route. 

Lastly, headways and span of service is one of the major factors into how much it costs to run MTA service. Sometimes, it is the cost that prevents MTA from giving the level of service riders deserve. However, improvements are constantly made to improve both headway and span of service. 

Next class: What is a Service Change?