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What's Driving You Crazy: The rules of solid white lines on city streets, interstates

Lane Line
Posted at 5:49 AM, May 11, 2021
and last updated 2021-05-12 06:22:51-04

Ed from Frederick writes, “What's driving you crazy? On the interstates you are not supposed to cross a solid white line. In the city all the turn only lanes are wholly marked with solid white lines. Why are city turn lanes not marked with short dashed lines like the exit only lanes on the interstate? Is it any wonder you see so many people breaking the law on the interstates?”

There is a misconception, by many drivers, that you are not allowed to cross a solid white line on or off the interstates. It is legal, although "discouraged," to cross a single solid white line. It is illegal to cross double white lines on or off the interstates.

All states, including Colorado, follow the guidance for roadway markings from the Federal Highway Administration's Manual on Uniform Traffic Control Devices (MUTCD). In Chapter 3B, Pavement and Curb Markings, in section 3B.04, Standard 20 it states, "Where crossing the lane line markings is discouraged, the lane line markings shall consist of a normal or wide solid white line.” In that same section at Standard 30 it states, “Where crossing the lane line markings is prohibited, the lane line markings shall consist of a solid double white line.”

I remember around 10 years ago talking to a person in Douglas County Public Works about the double white line feature they installed in parts of Highlands Ranch. It was done, they said, to protect bike riders in the bike lane from right turning drivers. The double white lines were painted just before an intersection where right turns on red were frequent. The lines prevented drivers stuck in a queue at a red light from moving over into the bike lane to make the right turn on red. The lines were removed several years later.

As for single solid white lines indicating turn lanes on city streets, the MUTCD guidance in section 3B.04.25 states, “On approaches to intersections, a solid white lane line marking should be used to separate a through lane from an added mandatory turn lane.” The key word in there is ‘should’.

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There is also guidance in subsection 6 that states, “A dotted white line marking shall be used as the lane line to separate a through lane that continues beyond the interchange or intersection from an adjacent lane for any of the following conditions: A deceleration or acceleration lane, a through lane that becomes a mandatory exit or turn lane, an auxiliary lane 2 miles or less in length between an entrance ramp and an exit ramp, or an auxiliary lane 1 mile or less in length between two adjacent intersections.”

Those rules can be modified where lane changes might cause conflicts. In those cases, a wide or normal solid white lane line may extend upstream from an intersection. And in the case of a lane drop at an exit ramp or intersection, such a solid white line may replace a portion, but not all of the length of the wide dotted white lane line.

The only specific instance I could find in the Colorado Revised Statutes regarding this issue is from CRS: 42-4-603: Obedience to official traffic control devices. “(1) No driver of a vehicle shall disobey the instructions of any official traffic control device including any official hand signal device placed or displayed in accordance with the provisions of this article unless otherwise directed by a police officer subject to the exceptions in this article granted the driver of an authorized emergency vehicle.”

Bottom line, pavement markings on city streets or on the interstates will lead you the right way if you are making a turn. And unless otherwise posted by a sign, in Colorado crossing a single white line is discouraged, but isn’t illegal.

Denver7 traffic anchor Jayson Luber says he has been covering Denver-metro traffic since Ben-Hur was driving a chariot. (We believe the actual number is over 20 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 Driving You Crazy podcast on iTunes , Stitcher , Google Play or Podbean.