Baltimore County News
Engineer I, Bureau of Traffic Engineering & Transportation Planning,
Department of Public Works
As traffic engineers in the County’s Department of Public Works, we know that in Baltimore County, like most places, many of us are trying to get to the same places – usually at around the same time of day. Ironically, it is in this so called “rush hour” that traffic slows down, and travel time delays are significantly increased. Amongst the signalized intersections throughout Baltimore County, there are certain ones which back up routinely, and at times drivers avoid them by cutting through residential neighborhoods or taking a completely different route to the destination.
Unfortunately as a result of population and development growth, traffic typically becomes more congested as years go by. Because of this, our traffic engineers need to regularly monitor and rate all signalized intersections in the County. Traffic counts and observations of queuing are taken into consideration for the evaluation. From the data, we would determine if any improvements to the intersection are necessary. Changes could include re-timing the signal, designating new lanes, or geometric changes such as adding islands or changing approaches so that traffic flows better.
Every year, Public Works traffic engineers rate intersections across the County from “A” to “F” –excellent to failing. These ratings are based on how well the traffic signal can provide service during rush hours. The intersections rated “A,” “B” or “C” are considered acceptable and are studied in rotation every three to four years. The “D” rating is considered a warning sign, and those rated “E” or “F are considered failing. The “D” “E” and “F” intersections are reviewed annually.
We report those marginal or failing intersections (“D” “E” and “F”) to the County’s Planning Board each January and then to the County Council. This ensures that everyone has an understanding of driving conditions on County roads. A failing intersection (“E” or “F”) may indicate slow or stalled traffic during rush hours and may explain why drivers are diverting to secondary streets. Failing grades may also mean that current conditions cannot support the construction of more new homes or shopping centers. When an intersection does not make the grade one year, it is re-examined the following year until an improvement can be engineered and implemented.
This “alphabet” rating system is a performance measure used by traffic engineers to assist in determining problematic areas and in keeping traffic moving in Baltimore County. Ultimately we build a categorical picture of the County’s intersections – one that allows us to spot problems, fix them and plan for the future. We hope that by monitoring and rating these intersections, we can help you get where you are going as efficiently as possible for years to come.
Engineer I, Public Works, Bureau of Traffic Engineering
Around 350 traffic signals are maintained by the Baltimore County Bureau of Traffic Engineering. Part of maintaining the signals is determining and programming signal timings to ensure that there are appropriate green times for the assigned movements so that traffic may flow efficiently. Traffic engineers determine the signal timings with assistance of a computer program called Synchro.
Synchro is a computer program that calculates the Level of Service (LOS) of an intersection based on traffic volumes, lane geometry and signal timings. Traffic volumes at an intersection are collected on one-year or three-year cycles depending on the severity of congestion. This traffic intersection data can be viewed on the County’s web site. The most heavily congested intersections are counted every year. At the same time, traffic engineers also verify the lane geometries and signal timings. If there is a proposal to change lane geometries, such as adding turn lanes or installing a roundabout or traffic signal, Synchro can determine if the proposed changes will improve the traffic flows at the intersection.
Because growth is natural and expected in metropolitan areas, traffic signal timings need to be revised from time to time to accommodate the change in traffic demands based on increases that are apparent from the traffic counts. Synchro is used to determine if signal timing changes are needed. However, achieving the lowest delay at a particular intersection does not necessarily represent the optimal signal timing, especially at coordinated signals, because the main objective is to move traffic through the corridor. In coordinated signal systems there is more green time given to the mainline traffic. Synchro can analyze a series of coordinated intersections and plot out a graph that shows how traffic flows from one intersection to the other. In addition, Synchro has an auxiliary program called Sim Traffic that can help visualize traffic flows.
Sim Traffic is a simulation software that takes data parameters from Synchro and puts them in an animated presentation. Roads and intersections are laid out in relative scale in top view, with simulated cars running through the intersections. Because flows from signals in a coordinated system are dependent on one another, it is good to see in action how the queues dissipate and move through the corridor, and where congestion tends to build up. Like the applications used in Synchro, we can also see how different lane geometries and signal timings affect the flow of traffic.
We can also make a comparison on the effectiveness of a proposed signal or roundabout at an existing intersection. This is very helpful because the animations visually show whether the changes create more congestion or improve traffic flow which can be very helpful when explaining traffic engineering decisions to the public.
Although Synchro and Sim Traffic are very helpful in determining timings, they are not a substitute for field observations. Ultimately, a field observation is necessary to verify improvements from timing changes, and further adjustments to timings will be done based on field observations. Synchro and Sim Traffic are not substitutes for engineering judgment; however they are great tools in the traffic engineer's tool box.
Revised April 6, 2016