There are potentially millions of roadway configurations. Complicating this is the fact that if you proceed a few feet down a given roadway it can change dramatically. Below is an example of how big a change there can be from one city block to the next.
The example above showcases the approach of East-West Highway as it intersects Rockville Pike in Downtown Bethesda, MD. At position 1 (in red), East-West Highway is a westbound oneway 3-lane undivided roadway. At position 2 (Yellow), East-West Highway has become a 5-lane divided roadway (with one lane of parking): doubling the width less than 400 feet. These stark changes to facilities affect the behaviors of drivers, bicyclists and pedestrians alike and it's important to capture the data as close to reality as possible to better evaluate the safety posture of any approach to a given intersection.
Major Components of a Cross-Section
The purpose of the LRS Cross-section at is to provide a data model that can capture these changes in a way that represents the real world, such as the example above. There are 3 primary components to a cross-section of the roadway.
In the real world, there are obvious sections of the roadway that have discrete purposes. We call these 'Section Types'. Section types could be anything in the roadway which serves a specific purpose in guiding and moving traffic: lanes, bike lanes, medians, buffers, etc. Each section has its purpose.
Of course, each section occupies a certain width of the roadway and this is a useful attribute to keep track of. Width is stored in feet and is approximate (usually measured from our imagery in GIS).
Direction represents the direction of a travel lane in reference to the ascending direction of the DDOT centerline geometry. For example, 16th Street NW ascends to the north because it is located in the NW quadrant; all data are oriented in a north-facing direction. Lanes are numbered from left to right in this same direction. The divider (usually a median or double-yellow stripe) divides the left side lanes from the right side lanes. Below is a north-facing photo example that illustrates this. Lanes 1,2 and 3 are to the left of the double-yellow stripe; lanes 4 and 5 are right side lanes.
Below is a graphical representation of a Streetmix view showing a hypothetical roadway:
|Cross-Section Type||Sidewalk||Bike: Bike and Bus Lane||Lane: Through|
Buffer: Curbed, Raised and Continuous
|Lane: Through and Left Turn||Parking: Parallel||Sidewalk|