In late 2022, I volunteered to serve on a traffic calming committee to recommend various strategies for creating a slower, safer design for the street we live on in Greenville. I asked a City engineer about whether the City would consider adding traffic circles at our street intersections.

The engineer told me that circles are a problem because they are seen as being an impediment to fire trucks.

If I had the opportunity to send a written response to this engineer, the following is what I would tell her.

It has been unquestionably established over the past few decades that horizontal interventions such as traffic circles significantly reduce crashes at intersections.

When fire truck objections prevent the installation of circles, overall city and neighborhood objectives are harmed because we end up suboptimizing the “needs” of the fire truck. A well-designed study conducted in Longmont CO by Peter Swift showed this conclusively.

In that study, Swift showed that when street dimensions were enlarged to produce faster fire truck response times, the injuries and deaths averted by faster fire trucks were far outweighed by the increase in passenger vehicle injuries and deaths caused by the enlarged street dimensions. This is because fire injuries and deaths are much more rare than vehicle injuries and deaths.

See: Swift and Associates. Residential Street Typology and Injury Accident Frequency. Longmont, Colo.: Peter Swift, 1997.

In other words, by suboptimizing on fire safety by speeding up fire trucks, we end up increasing the overall number of community injuries and deaths. Fire safety, you see, is a subcategory of the broader life safety. For a safer city and safer neighborhoods, then, the key is to focus on the umbrella of life safety rather than the subcategory of fire safety. That means our primary focus must be to use the smaller dimensions of streets and intersections which reliably deliver slower, safer, more attentive driving.

In sum, by designing our streets for the rare and oversized fire truck rather than the common, smaller-sized passenger vehicle, we end up dangerously oversizing our street dimensions by applying “worst case scenario” geometries for the rare large vehicle. Doing this drastically increases the likelihood of excessive speeds and excessive inattention by motorists due to “risk homeostasis,” whereby humans drive a vehicle at the highest possible speed (and devote the least amount of attentiveness) that allows them to still feel safe. This speed and inattentiveness ratchets up each time we increase the dimensions of intersections and roadways and clear zones. The result is a net increase in serious injuries and deaths in our community due to the increased likelihood of vehicle crashes caused by speeding and inattentiveness.

Designing our streets for the rare, oversized fire truck is therefore backward.

For a safer community, we must instead size our fire trucks to fit the design dimensions of a safe street. That has led several communities – particularly in Europe – to include in their fleet of fire trucks a set of smaller trucks so that they can nimbly navigate smaller, slower, safer neighborhood streets. That is, a street using a low design speed.

Which is, by far, the safest way to design a street.

In the rare event that it is not possible for a fire truck to promptly pass through a slower, safer intersection equipped with, say, a traffic circle, a common solution is to use a “mountable” curb or “apron” to wrap around the circle, which enables larger fire trucks to mount an apron that is much less mountable by a passenger vehicle.

______________________________

Use this link to purchase books published by Dom Nozzi.

Fire Trucks and Public Safety