Many developers come to our office with a simple question: “How do I get a traffic signal into my proposed development?” For the commercial site developer, the addition of a traffic signal at their site means easy access in and out for the eventual customers and, more importantly, makes getting lucrative leases for the commercial lots a whole lot easier. However, getting that traffic signal can sometimes be a difficult task and, in many cases, it just isn’t feasible.
One might assume our job is to simply put in a signal where requested. However, we must remember that traffic signals are controlled by municipalities, and we can only work within the regulatory parameters set by the local and state jurisdictions. We must also factor in pedestrian and safety concerns, which could easily fill a blog post on their own. Below are three hurdles to overcome before getting a traffic signal for your proposed development. (This is written particularly for the state of Georgia and GDOT, however most, if not all, of these will apply elsewhere.)
1. Produce enough traffic!
If you want a traffic signal you must produce enough traffic in and out of your development to constitute having one in the first place. The standard practice for determining the required traffic volume for a traffic signal is in the Manual on Uniform Traffic Control Devices (MUTCD). This manual contains the eight-hour traffic signal warrant, which, in a highly-generalized way, says you need X number of vehicles turning out of your development and Y number of vehicles going past your development, and that number needs to be met or exceeded for eight hours of the day. Typically, this will boil down to 600 vehicles per hour (vph) on the major road (both directions combined) and 150 vph on the minor road, or 900 vph on the major road and 75 vph on the minor road. To make things even more difficult, typically all right-turns leaving the development can’t be included in this number since they rarely have to wait too long either way. Reaching these thresholds for most developments usually involves multiple fast-food restaurants, coffee shops, or a large gas station.
2. Traffic Signal Spacing
If you have the required traffic volume, your next hurdle is likely to be that your driveway is too close to the next traffic signal. When traffic signals are placed too close together it can cause congestion and impede the flow of traffic on the major road where they’re located. Keep in mind that the Department of Transportation is more concerned with keeping the roadways moving, and sometimes that means a traffic signal in the proposed location isn't going to work. For GDOT, this spacing is recommended to be 1,320 feet in rural areas and 1,000 feet in urban areas. It is possible to get this shortened, but it is an uphill battle from Day 1 to get approval. So if you have the space, use it wisely.
3. Driveway Alignment
One of the factors that we have seen kill a proposed traffic signal is the driveway alignment. This is something that is rarely thought about until the rest of the site is already done and it is “too late” to change it. If you want a full-access driveway, and especially a signal, and there is a full-access driveway / signal on the other side of the road, they need to line up! This is particularly important for the through lanes. Sometimes a slight offset can be manageable, but it will likely not be approved if it is off by more than a couple of feet.
There are quite a bit more reasons your traffic signal may or may not be approved, but these are the three major issues we see on almost every project. Why is it so hard to get a traffic signal? It is so difficult because often the governing body giving you approval is going to have to maintain that signal and that costs time and money for as long as that intersection exists. When we saw the economic downturn, many of the proposed developments fell through after they put in a traffic signal, leaving the government stuck footing the bill for a signal that didn’t need to be there. Also, if a traffic signal doesn’t really make sense for the location, it is going to slow down the roadway network around it, which the DOT has to keep moving. These, along with some other considerations, has made it a bit more difficult to get a traffic signal approved.
If you are considering a traffic signal for your development, give us a call or send us an email and we can walk you through the process and work on designing one for you.
About Blake Bredbenner
Blake Bredbenner, EIT is a Transportation Project Analyst for Foresite Group’s Transportation Division in Norcross, GA. Blake graduated from the Georgia Institute of Technology with his Bachelor’s degree in Civil Engineering. Blake particularly enjoys his work in operations and optimization including traffic signal timing, forecasting, and design alternatives.