A month ago I wrote the 10 Things a New City Traffic Engineer Should Do. First on my list is reviewing the city’s transportation plan. Here are key items that should be included the plan and the new traffic engineer should think through –
- Access Spacing Guidelines: First on my list because you’re going to be applying these rules to the new site plans you review. There might be a development plan sitting on your desk the first day on the job. You also need to make sure the city guidelines dovetail with county and state guidelines.
- Right-of-way Guidelines: Also important for site plan review. This defines how much public right-of-way the development should be dedicating along each street corridor.
- Functional Classification System: At a minimum, the streets within the city should be broken up into arterials, minor-arterials, collectors and local streets. Typically the arterials are under the state jurisdiction, minor-arterials are largely county roads but may be a state road or two, collectors are primarily under the jurisdiction of the city but may be a county road or two, and local streets are all city. This system map will give you a snapshot of your system. Even if you have a lot of cul-de-sacs in the local neighborhoods, hopefully you have a reasonable grid system of higher order roads to move traffic around town. The city traffic engineer typically focuses the most attention on the intersections of minor-arterial to minor arterial, minor arterial to collector, and collector to collector.
- Existing Daily Traffic Volumes: Cross reference these volumes to the functional classification system map. Hopefully you don’t have any collectors with 25,000 cars a day. Really rough guidelines: collectors should carry 1,000 to 15,000 cars per day, minor-arterials should care 15,000 to 35,000 cars per day and arterials should carry 35,0000+ cars per day and often more than 100,000 on urban freeways. You probably have some issues if you have local streets carrying much more than 1,000 cars a day. The transportation plan may be five to ten years old and the existing data in their will match the vintage of publication. Check your most current daily volumes against both the “existing” volumes in the report and the 20 year forecasts.
- 20 Year Traffic Forecasts: Hopefully these forecasts are tied to the city’s land use plan, but in smaller cities all of the forecasts may just be the existing volumes multiplied be a factor (such as 1.5). Spend time reconstructing the development that’s occurred since the forecasts were prepared. Also think through the underlying assumptions in the forecasts. A 25 year trendline was broken by the recession that we are climbing out of.
- Capacity Issues: The daily capacity volumes of different roadway cross sections (from the Highway Capacity Manual) was probably applied against the existing and 20 year forecasts to highlight corridors that are or may become congested. Scrutinize this list based on the capacities from the current HCM (2010) if the plan used capacities from the 2000 HCM. Also cross-reference the issues against all of the different traffic volume data sets you’ve reviewed.
- Safety Hot Spots: Many transportation plans don’t include crash data, but I think the better plans do. Again, if the plan is pretty old, make sure you get current data.
- Multi-Modal Issues: Airports, harbors, rail and transit may be in the plan, but these areas are typically outside the control of the city and they take coordination with other government entities. The traffic engineer should be generally aware of these modes. Other angles of multi-modal are bicycle and pedestrian facilities as well as context sensitive design. Hopefully the transportation plan includes maps/plans related to trails and sidewalks. The transportation plan probably doesn’t include discussions related to how transportation systems are flexibly designed to fit the context of the area, but this concept has been around for more than a decade and could be included in the plan. At a minimum, context sensitive design is a topic the traffic engineer should discuss with the city engineer.
- Capital Improvement Plan (CIP): This should be a rolling five year improvement plan that is informed by the Capacity Issues and Safety Hot Spots sections of the plan. The CIP is a very big deal at the city. The traffic engineer will likely have some input, but this is a plan developed by the city engineer/public works director and will be discussed/approved by the city council. Think through the plan and try to identify issues that have been identified that are based on bad assumptions.
Please add your thoughts in the comments section…..