Driving You Crazy: Why is Ralston Road in Arvada between Wadsworth and Lamar two different speed limits?

ARVADA, Colo. — William from Arvada writes, “What's driving you crazy? Ralston Road in Arvada between the Wadsworth Bypass and Lamar Street. If you are going west, the speed limit is 40 mph. If you are going east the speed limit is 35 mph. I pointed this out to the city with no results. The curious part is that it doesn’t matter as the traffic on Ralston Road either direction is always doing at least 45 to 50.”

I think we should call this the curious case of the missing sign. Let me explain.

Municipalities have the option to determine what speed limit would be appropriate for any given roadway. Most rely on something called the 85^th percentile speed. That is the speed at which most people are driving and that number changes over time based on many factors like population, land use and enforcement. The speed limits on this mile and a quarter long section of Ralston Road were set years ago based on those historical conditions. When I reached out to Arvada’s traffic team, I was originally told that the current members couldn’t speak to the rationale for the split speed limits that are currently in place because they were not involved in the decision-making process.

Then I drove that section of Ralston Road each way, looking for reasons why the speed limits were set differently. My initial thought was the eastbound speed limit was left at 35 mph since that is the speed limit coming out of Olde Town Arvada west of Wadsworth. I dug deeper and went back in time, courtesy of Google Street view. It was there that I noticed that at least up to October 2019, there used to be a 40 mph speed limit sign on a light pole about 50 feet east of Wadsworth. That speed limit sign was missing from the next street view image taken in November 2020.

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The way speed limits work is you are supposed to obey the last sign you see until you see another sign. Since the old increased speed limit sign is not there — either by accident or on purpose — by default, the speed limit continues to be 35 mph until the next sign which is just after Lamar Street where the sign indicates the speed increases to 45 mph.

I again went back to the Arvada traffic team and asked about the missing speed limit sign. They said, “You are correct. This was a case of a missing sign. It looks like the pole was replaced at some point and perhaps the sign was not. The team is planning to get it reinstalled!”

They told me, they were going to replace the sign the day after my conversation with them. I went out a few days later and confirmed it was replaced. My GPS, however, didn’t read this story yet so it still shows the speed limit as 35 mph for now.

Separately from this, the traffic team toold me they are looking into all of the speed limits around Arvada as part of their Speed Management Plan. I’m told that the first phase of this effort kicked off this month with a focus on local and neighborhood roads. That could take much of 2026 to complete. Then phase 2 will come in 2027 and be an active study of larger arterial roads.

Traffic engineers will look at changes in land use in the area, road type and design, and the presence of vulnerable road users like transit riders, pedestrians and cyclists when determining the appropriate speed limit for any particular street.

The city said speed limits will be reviewed for consistency and apply a clear, criteria based framework for deciding speed limits in coordination with the Adams County Safety Action Plan, which includes both the Jefferson and Adams County portions of Arvada. The city said this effort will improve consistency across the entire city.

The city will also look at enhancing their adaptive speed limit program. Adaptive speed systems and limiters are already installed in newer vehicles and they read speed limit signs, verify that with GPS data to keep your car from going over that legal limit. In the short term, the traffic team will be maintaining the existing speed limits while this larger effort is completed. This process could take most of 2027 to complete.

Denver7 Traffic Expert Jayson Luber says he has been covering Denver-metro traffic since Ben-Hur was driving a chariot. (We believe the actual number is over 25 years.) He's obsessed with letting viewers know what's happening on their drive and the best way to avoid the problems that spring up. Follow him on Facebook, Twitter or Instagram or listen to his award winning Driving You Crazy podcast on any podcast app including iTunes, iHeartRadio, Spotify, Podbean, or YouTube.