What does the COVID-19 shutdown mean for traffic engineering in the short-term?

Since this nationwide shutdown of non-essential work (and workers) has now been in effect in many areas for over a month now, it has become clear to traffic engineers, DOTs (state and local), and county and municipal staffs that traffic data is going to be an issue both now and in the months to come.

It is also apparent that any attempt at counting traffic (either turning movements or AADT counts) at the present time would provide meaningless data. But why is this data meaningless?

First, the counts are much lower than what was observed on the same roadways and at the same intersections before the shutdowns occurred. This much should be obvious to anyone who has ventured out, even occasionally.

Second, the counts have not lowered in a predictable manner. Since not all businesses are shut down, and those that have remained open have been updating operating hours and practices on an on-going basis, a count taken two weeks ago may bear no resemblance to a count taken next week. This variability is far beyond what would normally be acceptable in traffic counts.

Third, the maturation of the “shelter-in-place” order will result in additional shifts in traffic patterns. Psychologically, the concept of a risk profile needs to come into consideration. Initially, most everyone felt that COVID-19 was a substantial risk to their health. They heeded the order to shelter at home and not venture out, except for essential needs. While not everyone followed this guidance, the vast majority did, which resulted in the substantial decreases in traffic.

In traffic engineering, one of the most common examples of a shifting risk profile is a driver waiting to make a left turn onto a busy road. A driver will wait for an acceptable gap in cross traffic to make the maneuver, but the longer they wait, the shorter the gap that is “acceptable” will become. Similarly, as the “shelter-in-place” order as matured, individuals are adjusting their risk profiles and are slowly taking on greater risk through venturing out of the home – often driven by a separate feeling: “cabin fever”. This innate desire just to get out of the house, even if to just drive around aimlessly, is slowly raising the amount of traffic seen on the roads again, but at unpredictable times.

Since the ability to measure traffic in a useful manner is essential to performing any traffic engineering study, how can any work be performed now?

Fortunately, many locations have been counted in the past few years. State DOTs, counties, and municipalities have programs that perform counts at many locations on an on-going basis, and this data can be publicly available. When a location was previously counted for a traffic study, reviewing agencies are aware, and can be helpful in connecting firms to share count data. There are also techniques to use existing counts at surrounding intersections to interpolate traffic and movements at an uncounted intersection. At RKA, we have staff experienced in this tricky interpolation process.

The only caveat to using “old” data is that we really do not know when traffic will return to “normal” or even exactly what that “normal” may look like. Unfortunately, the news tells us about many small businesses that may not be able to reopen as a result of this shutdown. We also do not know how the reopening of the economy will proceed. Most likely it will entail a slow scale-up, with restrictions being lifted in stages. This scale-up will permit businesses to reopen, but likely far below the scale they were accustomed to pre-shutdown. This will result in continual increases and shifts in traffic patterns for a longer-term period. As a result, we will not be able to apply a single positive/negative growth percentage (or scaling factor) like we normally would in order to adjust counts from one year to another.

This will be our new normal for quite a while, and we can probably expect that traffic data that was once quickly approved may instead take multiple iterations to settle upon final values. We can only apply our best engineering judgment and work closely with reviewing agencies to develop numbers that are acceptable to all involved.