Traffic Signal Level-of-Service
The level-of-service of an intersection is determined by analyzing each approach individually. A computation is made of each approach to determine its load factor (LF) during both the morning and afternoon peak hours. The LF is determined by recording the number of loaded cycles on each approach during the two-hour study periods in the morning and afternoon. View the level-of-service (PDF) for signaled intersections in Baltimore County.
Cycle of the Signal
A cycle of the signal is the period that encompasses one green indication. During each cycle of the traffic signal, an observer determines which vehicle is the last vehicle stopped in the queue at the time the signal turns green. If that last vehicle does not get through the intersection during that one green indication, the cycle is recorded as being loaded. This continues through an entire two-hour study period, with each approach of the intersection being independently evaluated.
Each approach is studied to determine the particular 60-minute period that had the highest percentage of cycles which were loaded. Thus each approach is given a separate maximum percentage of loaded cycles, and this percentage is called the load factor.
The load factor can range from zero percent to 100 percent. If an approach had a load factor of 40 percent, it would mean that during 40 percent of the cycles (in the most congested 60-minute period on that approach) all of the vehicles stopped in line for the signal when it changed green did not get through that signal. If there were 25 vehicles in the queue at the time the signal changed green and the last vehicle was the only one that did not get through the intersection the cycle would still be recorded as a loaded cycle.
The load factor for the intersection is determined by looking at the approach with the highest load factor in the morning and the same in the afternoon. The highest load factor for the morning and afternoon is then used to determine the level-of-service. In timing signals, it is the intent to try and equalize the load factor on each approach to be as equal as possible so that no one approach is being delayed more than the other. Therefore, if an intersection was evaluated and determined to have a load factor on one approach of 15 percent and on the cross-street approach of 60 percent, the signal would first be retimed to try and equalize them and then the intersection would be restudied.
The Level-of-Service is determined by using the following chart with the load factor for the intersection as computed above:
1% to 10%
11% to 30%
31% to 70%
71% to 85%
86% to 100%
In Baltimore County, the level-of-service can regulate the issuance of building permits for non-industrial development in urban areas determined to have a significant influence on a particular intersection.
- Level-of-Service D
Level-of-Service D intersections do not control issuance of building permits, but their areas are identified on Baltimore County's Basic Services Transportation Maps to identify the deficiency. The purpose of identifying D intersections is to provide notice to the public that the intersection has the potential of going to an E or F.
- Level-of-Service E
Areas around a level-of-service E intersection would be allowed to have a limited number of building permits issued.
- Level-of-Service F
Areas around a level-of-service F intersection would have a moratorium on building permits for non-industrial development, with some very limited exceptions.
Identifying these intersections also allows the County an opportunity to work toward correcting them and lessen congestion before it becomes a serious problem. The level-of-service does not in any way evaluate the safety aspects of an intersection but is strictly a congestion measure.
Revised January 27, 2016