TxDOT is seriously considering abandoning the 85th percentile rule

Texas continues to lead the nation in traffic deaths, with traffic deaths actually increasing in 2020, even though Texans were driving significantly less last year than the year before. Many believe that our high rates of traffic deaths have a lot to do with dangerous speeds that many Texans use when driving cars and trucks.

Many in the transportation engineering world believe that changing the design of streets and our speed limits is necessary to change our behavior. We want it to feel normal and intuitive to drive cars and trucks in Texas at safe speeds appropriate for whatever context we are in. Yet many of our streets and highways are designed in ways that actually encourage us to drive faster, and Texas has some of the highest speed limits in the country.

At the 2020 World Day of Remembrance for the Victims of Traffic Violence, we asked TXDOT to abandon the 85th percentile rule, as one of three major activist priorities for the state and local governments to address the danger of speed on Texas streets and roads. Lance Hamm of Vision Zero South Texas presented the case for abandoning the 85th Percentile Rule.

At the January 27, 2021 meeting of the Texas Transportation Commission, Michael A. Chacon, P.E. Director of TxDOT’s Traffic Safety Division presented on TXDOT’s existing methods for setting speed limits and the potential for improvements to this system, as shown in the following pdf and video from the meeting.

TexasTransportationCommission012721_Speed

At the Texas Transportation Forum on February 9, 2021, TxDOT Executive Director James Bass discussed the shift in TxDOT thinking directly. The video from the forum is not posted publicly, but here is a transcript of what he said when asked about the increase in traffic deaths in 2020.

“Yeah so one thing, it’s really disappointing, like you said, with the decrease in traffic volumes we were hoping to see a corresponding decrease in the number of fatalities.

And actually we’ve seen quite the opposite, In 2019, we had 3623 fatalities on Texas roads and as of this morning, in 2020, we had seen 3900. So 277 more with fewer people out on the road traveling. Now early on in the pandemic, I think traffic volumes were down 35, 40, 45%, in those early days. More recently we’ve seen traffic volumes be down closer to just 5%.

My belief is even though the traffic volumes may be getting back to quote unquote normal, I think that traffic may be spread more throughout the day than it was pre-pandemic. And with the traffic spread out more, it’s allowed more individuals to drive faster. And speed, you know, physics comes into play, and speed is a large contributor to you know fatal accidents.

And so one of the things we’ve been working on at TXDOT is really looking at how we set our speed limits. The old rule of thumb is the 85th percentile that’s probably been around forever, and ever,  there are new methodologies that are being researched and investigated, and we are kind of keeping our eyes on that.

And you know personal behavior has changed over the decades, and it may have been that 85% of people drove safely decades ago. I’m not 100% sure that that’s the case today, so I think that we need to, you know, as we always do, look for new ways to improve our operations and look at different things.

And another thing, kind of um you know once I became executive director, I had a new perspective and um driving across the state and looking at different roadways and I’m sure there are roadways out there that are two lane roadways with little shoulders and the speed limit is likely posted at 70 or 75 mph.

And then you get on an interstate with all of its safety enhancements in there and its got the same speed limit. And that just doesn’t equate well in a logical frame of mind, that those roadways could be posted at the same speed limit.

Now it may be that people are able or that 85% of people drive the same speed, now again I’m not sure that that is truly a safe speed on both of those roadways and so one of the things I think if maybe we could look at the characteristics of a roadway. Is it two lane or is it four lane divided, four lane undivided, what are the shoulders, and maybe look at those characteristics of the roadway and look at possibly setting maximum speed limits based upon the characteristics of the roadways.”

– TxDOT Executive Director James Bass, February 9, 2021