How Networks Work
Note: This article was originally published August 2004. The data is out-of-date. We believe that the basic argument remains sound.
A well-designed network is the basis for any successful transportation service. Unfortunately, the importance of networks has received little attention from transportation planners.
Most passenger rail planning to date has addressed individual routes. The pattern has been to identify two or three cities less than 500 miles apart and look at potential traffic between those cities.
The Midwest Regional Rail Initiative was the first study to look at the synergies of an integrated network. It showed that ridership increases and unit costs decrease when routes are operated together. California has demonstrated that integrated bus connections will build ridership further.
A simple example explains why network connections are important. Two five-stop routes operated independently serve a total of eighteen city pairs. If integrated, they serve thirty-six, a significantly greater market upon which to draw.
Reconnecting America has focused attention on the need to build strong connections among airlines, bus lines and railroads. The principle is the same. Connecting a rail route to an air route creates more opportunities for travelers to use the system, increasing the volume on both.
This article will give specific examples of how networks can be enhanced to create additional volume.
Networks consist of nodes (stations) and routes. Nodes either gather volume for the network or serve as a transfer points between routes or perform both functions.
A hub is technically the center node in a hub-and-spoke network, but the term is often used to describe any high-volume transportation node.
The purpose of a railroad station is to gather travelers from as wide an area as possible. In addition to foot traffic, volume can be gathered with connections to local transit systems and good highway access. Often railroad functions can be combined with other functions to create further economies of scale while making the station more attractive.
An ancillary benefit is that the area surrounding an intermodal center can support a higher level of development than an area served only by highways. This results in higher real estate values, a stronger community and a larger customer base for the railroad service.
A Well Designed Station
The recently constructed station in Champaign, IL has all the key elements of a successful railroad station.
1) excellent pedestrian access from the downtown,
2) secure bike racks,
3) local transit connections,
4) intercity bus service,
5) good highway access and a large, secure parking lot.
It also has meeting facilities and an alternative school to increase foot traffic in and around the station.
Because of these features it is able to attract railroad passengers from a large geographic area.
The Baltimore/Washington International airport station provides an example of how stations can bundle trip types.
The station was built primarily for airport users travelling to or from Washington, DC. The airport related volume alone is probably sufficient to warrant a medium level of service.
Ridership improved dramatically when a large parking garage was constructed. Daily commuters justify a higher number of train frequencies, which attract even more air travelers. BWI now supports a very high level of service, including 125-mph MARC express trains to DC. Even many Acela Express trains stop at BWI (but not at Newark International).
In a railroad network, nodes are connected by track. While much less expensive to build and maintain than the equivalent highway capacity, high-quality track requires substantial up-front investment.
The volume required to justify that investment can be built in many ways.
The high-speed lines in France serve as the very high-volume trunks in an extensive network that branches off into Italy, Germany, Spain and England.
In the Northeast Corridor extensive commuter operations provide substantial base volume.
Put nodes and links together, and you have a network. There are many kinds of networks, each with its own strengths and advantages. Several relate to railroad service.
In its purest form a point to point network involves two nodes connected by a single link.Discount airlines are often called point-to-point carriers. The belief is that each route is planned separately. In truth, few airline networks are this simple. Connections are well planned in order to gather passengers destined to multiple destinations into a single, more efficient plane.
The Paul Revere network gets its name from the patriot’s famous ride. He had to reach several points as quickly as possible and so drew the shortest line between them.
Taken independently from each other, almost all passenger train routes are Paul Revere networks. These build volume by increasing the total number of possible trip combinations. All other factors being equal, lengthening a route will increase volume by increasing the total number of possible trips. Increasing frequency and reducing trip time will also increase volume.
Amtrak's Texas Eagle provides an example of how distance can build volume. Currently, the train runs seven days a week between Chicago and San Antonio. Three days a week two cars connect at San Antonio with the Sunset Limited to Los Angeles. Volume increases on the Texas Eagle portion of the run by 39% on the days that connection is made.
Much of the additional volume is made up of passengers traveling from Arkansas to points west of Texas, a market not well served by air.
The New Haven––Springfield route illustrates the value of frequency. On April 18, 2003 Amtrak increased frequency on the New Haven, CT to Springfield, MA line from 11 daily departures to 16. The additional frequencies, combined with a fare reduction, have led to a 38% increase in local ridership. Additionally, the volume of passengers connecting between the Springfield line and the Northeast Corridor at New Haven has increased to about 50% of the Springfield line's volume.
A pure hub-and-spoke network has is a single central node, called a hub, at which all routes converge. To get from one point on the network to any other point requires a trip through the hub.
A hub-and-spoke network is very effective in building economies of scale. For example, linking five cities would require ten point-to-point flights. A hub- and-spoke network linking those same five cities would only require four.
Ironically, several so-called point-to- point carriers operate hub and spoke networks. Airtran and Independence Air are two examples.
Passengers using these carriers are willing to accept longer transit times in exchange for the lower fares made possible by the networks efficiencies.
The networks of the so-called hub airlines are actually hierarchal networks, small planes feed passengers to big planes operating on high-volume trunk routes.
The virtue of this model is that the trunk routes can utilize larger, more efficient planes. The downside is that the feeder lines can be costly to operate. Often the feeder flights are subsidized by the trunk routes.
Several factors have caused a reduction in feeder flights in the last decade. The shift to regional jets raised the threshold volume for feeder flights, operating costs have increased in general and passenger travel has declined. Result: smaller cities have lost service and volumes have been reduced on the trunks.
Trains can fill the gap by providing a more cost-effective method of feeder passengers into major hubs.
This is happening now at Newark International Airport. When airport opened a new station served by Amtrak's Northeast Corridor trains, Continental Airlines entered into a joint ticketing arrangement with Amtrak.
This simple connection helped both Amtrak and Continental. Amtrak added volume to existing trains. Continental gained more frequent feeder service and can now use its valuable runway slots to handle larger, long-haul planes.
As networks become more complex the total number of city pairs begins to grow in multiples. Grid networks offer the next level of complexity and connectivity. Fashioned like a tic-tac-toe board, each cross point on the network becomes a transfer node. Not only do possible city pairs increase, but multiple paths become available – offering redundancy to route around congestion or network outages.
The internet is based on the grid model. The multiple paths make it allow the network to continue to function even if individual nodes or links are removed. Both Southwest and Greyhound operate networks that follow this model.
Network design is a critical part of creating an effective transportation system. Different networks achieve diff e rent ends, but they all accomplish the same goal: creating more opportunities for travelers to use the system while increasing volume and building economies of scale.