Colorado Highway Quickfacts

Driving Laws | Highway Financing | Winter Driving | CDOT
Route Numbering & Marking | Structure Numbers | NHS

Colorado Driving Laws

Some of the driving laws in Colorado:

Speed Limits
The blanket law for Colorado is "reasonable and prudent", meaning don't go faster than is safe for conditions. In addition to that, limits for certain areas, unless otherwise posted, are:

Home-rule cities can also adopt a blanket speed limit for the whole town, such as 25 mph, and it will be that unless otherwise posted.

Minimum speeds are required so that drivers are going fast enough such that they are not impeding or blocking the "normal and reasonable" flow of traffic. Colorado also has a "move right" law, saying that on a divided highway with a 65 mph or higher speed limit, the left lane can only be used for passing when traffic is light enough.

Minimum speed limits can also be posted, but there aren't too many of those in the state.

Remember that no matter how good the conditions may be, if one is going faster than what is posted, it's considered a violation. It can also be a violation to be going the speed limit when that is too fast for conditions (such as screaming along at 75 in a blizzard or heavy traffic). Fines for speeding can also be doubled or subject to a minimum fine along zones posted as such. Cities can adopt ordinances to double or have minimum fines in certain areas, such as school zones. Statewide, fines are double in construction zones when posted as such.

Other Traffic Laws

Seat Belts

Exceptions to the seat belt law include ambulance and police workers, people with physical/psychological disabilities that get approval, buses, and mail carriers/delivery drivers.

Driving Under the Influence
A person is considered driving under the influence (DUI) if they have a blood alcohol content of 0.08 or above. A BAC of 0.05 is driving while ability impaired (DWAI).

The DUI BAC was lowered from 0.10 to 0.08 on July 1, 2004. It probably wouldn't have happened if not for the pressure of losing federal highway funds if it wasn't lowered.

License Plates & Registration
Vehicle titles and registration in Colorado are done through the county in which you reside. Check the blue pages in the phone book for "Clerk" or "Motor Vehicle" for your county. Colorado requires that people moving to the state get their vehicles registered here within 30 days of establishing residency. Proof of insurance, title, and VIN is required.

Emissions Testing: Emissions testing is required for gasoline and diesel vehicles in all of Boulder, Broomfield, Denver, Douglas and Jefferson Counties as well as the western parts of Adams and Arapahoe Counties, and some portions of Larimer and Weld Counties. Emissions testing is done by EnviroTest at several dozen locations. A vehicle must be tested every two years once a new vehicle reaches seven years old, or before that two year mark if it changes ownership. Intervals are different for diesel vehicles and vehicles 1981 and older. If it's time for your vehicle to be tested it will be indicated on your registration renewal card.

Colorado's standard passenger car plate. Prior to mid-1999 the plate had the colors reversed and an alphanumeric system of ABC1234. In the current 123 ABC format, the first letter of the three letters shows how old the plate is. The system started with A in 1999, then worked up through the alphabet with Z  expected to the be reached in 2012, exhausting the current combination. After that Q will be used, since it wasn't in the initial run until the state could solve design issues with the look of the Q. After that it is expected the combination will be reversed to ABC 123.

The light truck plate, for pickups, SUVs, and other vehicles up to 16,000 lbs.

For persons with disabilities.

The "designer" plate, which has a niftier design.

There are dozens of different types of plates, including college, military, government, and special interest plates (you can advertise to the world you're a member of a Masonic Lodge if you so desire). Some have fees above the standard rate. Plates are required for both the front and back of the vehicle, although the yearly sticker only goes on the back.

Driver's Licenses
Colorado driver's licenses are obtained through offices of the Department of Revenue. Look under "Revenue Department of" of the state in the blue pages. Out-of-staters moving in can obtain a Colorado license by presenting the valid license from the other state. No written test is required, only a vision check. Colorado also has a motor voter system, so you should register to vote at the same time. Standard licenses require renewal every 10 years.

Graduated Driver's Licenses: Persons 15 to 21 years old must go through the graduated license process, which can be started any time after reaching age 15.

Anyone on a permit is prohibited from using a cell phone while driving. When under 18, for the first six months you have your minor license you cannot have a passenger under 21 unless there is someone 21 or over in the car or the person under 21 is family. From 6 months to 1 year on your minor license you are allowed 1 passenger under 21 (same exemptions). Also, if under 18, for the first year you have your minor license you cannot drive from 12 a.m. to 5 a.m. unless there's someone over 21 in the car or it's school/work-related.


Highway Financing in Colorado

Colorado raises funds for state highway maintenance and construction through three main forms: The gasoline tax, vehicle registration fees, and supplemental funds from the general state sales tax ("Senate Bill 1 funds").

The money is dumped into the state highway users fund and is distributed as follows:


Winter Driving in Colorado

Colorado has mountains and is subject to a continental climate. Both result in snow. Anyone who lives in other winter-prone states should not be afraid of driving in winter weather in Colorado. Just because Colorado has mountains does not make for some kind of special form of winter weather that would frighten out-of-staters.

The same rules apply to winter driving in Colorado as apply to winter driving everywhere else:

  1. Slow down in slick conditions.
  2. Have a safe following distance between you and the car in front of you. It should be up as high as four seconds in bad conditions.
  3. Make sure your vehicle is in good working order, with properly inflated tires, windshield washer fluid and an ice scraper.
  4. Slow down in slick conditions.
  5. Have decent all-season tires, or snow tires if you feel like spending the extra money.
  6. Plan ahead. Know your route. Get weather reports.
  7. Just because you have four-wheel drive and/or anti-lock brakes does not mean your car is immune from the laws of physics.
  8. Slow down in slick conditions.
  9. If you're driving in a storm and feel as though you're in over your head, that's a sign you should stop.
  10. Slow down in slick conditions.

The I-70 Corridor
Passing through Colorado on I-70 during the winter? Don't be scared. But I sure get a lot of e-mails from people who sound like they are. People hear "I-70" and "Colorado" and immediately think of the mountains, but one has to remember that over 150 miles of I-70 in Colorado look just like Kansas. Really there are only three mountainous areas along I-70 to be concerned about: Mount Vernon Canyon between Golden and Idaho Springs, Eisenhower Tunnel/Straight Creek Canyon, and Vail Pass. Each can see severe winter weather, but CDOT does a good job keeping a handle on things. Unless you're passing through one of those areas during the height of or immediately after a storm, don't expect problems.

Winter Closures
Several major roadways in Colorado close for the entire winter (approximately October to May):

Other short-term closures during the height of a storm may take place. These areas include many of the passes plus the Eastern Plains.

Pikes Peak is open year-round conditions permitting.

Road Treatments
CDOT uses two main road treatments: Salt/sand and liquid de-icers (magnesium chloride, M1000, or Ice Slicer). CDOT is beginning to use more liquid de-icers, since it does not contribute to airborne particulates, does not cause silt runoff into streams, and can be applied before a storm. More can be found about road treatments through the links below.

Chains Laws
Chain laws in Colorado are divided between commercial vehicles and noncommercial vehicles.

Commercial Vehicles (includes buses). Commercial vehicles are defined as vehicles engaged in commercial transportation of cargo or passengers and

When the chain law is in effect applying to commercial vehicles, the requirements for chains may differ between single-axle drive and double-axle drive tractors. Provisions also allow "alternative traction devices", such as automatic wheel sanders. Trucks that travel I-70 between Edwards and Golden from September 1 to May 31 are required to carry chains on board to use if needed. Oversize/overweight permit trucks cannot travel in an area where the chain law is in effect.

Noncommercial Vehicles. For noncommercial vehicles when the chain law is implemented, one of two possible levels is called for.

Passes in Colorado most likely to see chain laws for non-commercial vehicles are the US 550 passes, Lizard Head, Slumgullion, Monarch and Wolf Creek. These are also the passes most often closed during the winter.

The chain law discontinues when either bare pavement is encountered or signs advise it has ended. A violation has a fine of $500, and that can jump to $1000 if the violation results in blocked traffic. Studded tires are allowed year-round in Colorado. More on Colorado's chain law can be found through the links below. Thanks to Dave Armbruster for getting information to me on this topic.

Accident Alert
Accident Alert is a protocol that law enforcement agencies enact when a winter storm causes so many accidents it has the potential to overwhelm the police force. When Accident Alert is active, it's made known by the broadcast media. Under Accident Alert, police will not respond to minor accidents that involve only minor property damage. If you're involved in a minor accident that has no injuries during Accident Alert, exchange information at the scene and then report it to the necessary police agency within a day or two. Don't bother waiting for the cops to show up.

Snow Emergency Routes, Alternate Side Parking, Plow Priority Routes
Plowing and winter parking practices vary from city to city. Consult your local ordinances.

More Winter Driving Information (Official Sources)


The Colorado Department of Transportation

The Colorado Department of Transportation (CDOT) manages approximately 9,000 miles of highway in the state. According to CDOT, the system handles over 23 billion vehicle miles of travel each year. Interstate routes account for only about 10 percent of the total mileage on the state system, but 40 percent of all travel takes place on the Interstates.

CDOT is headed by an executive director, appointed by the governor. The director reports on issues to the governor, the legislature, and the Colorado Transporation Commission. The CTC approves CDOT budgets, major projects, and sets overall policy. The CTC is made up of members from 11 districts and are appointed by the governor.

CDOT's state headquarters are at 4201 E. Arkansas Avenue, Denver (303-757-9011). CDOT is subdivided into five regions, with maintenance and day-to-day engineering and projects being administered at that level. These regions run out of dozens of engineering and maintenance offices scattered around the state.

Region HQs:

CDOT reorginzed its regions in spring 2013. Prior to that there were 6, with Region 6 being just metro Denver. The reorganization shuffled the boundaries of Regions 1, 2 and 4 to dissolve 6.


Route Numbering and Marking

The modern version of the Colorado state highway system traces its roots to 1923, when the state marked highways with numbers. At first, there was a system with the lower numbers for major cross-state routes, and an almost rock-solid adherence to even numbers going east-west and odd numbers going north-south. In 1927 the US routes came, and those were marked concurrent along their routing with the state highways. In 1960 the Interstate highways were first marked, spelling the doom for some state and US highways. See my History of Colorado Roads page to learn more about route numbering.

In addition to the state-maintained highway system, Colorado also has county-maintained highways, city municipal streets, and grassland/forest roads maintained by whichever national park/forest/grassland you're in. Colorado has no townships like Midwestern states, so there are no township-maintained roads. All roads outside of city limits that are not state highways and are not a National Forest/Park road are county roads.

Colorado uses business routes with reckless abandon. In the case of US routes, in most cases there was some sort of bypass of a town built, and the through-town route was given the BR designation. US 34, 85, and 160 have BRs. As to Interstate business loops, in these cases there is usually a business loop run concurrently with the US highway that runs with the Interstate. Each Interstate in Colorado has business loops or business spurs.

For a history of route markers in Colorado go to my Route Markers page.

For a look at county route markers go to the County Road Numbering page.

Exit Numbers and Mileposts
Colorado mileposts all of its state-maintained highways. These start at the south or west end of the highway, and count up. Standard vertical white-on-green mileposts are used. On two lane highways, there will be two facing in each direction on a single post on one side of the road, but there will be two separate ones for each direction on divided highways.

Colorado uses milepost-based exit numbering for its Interstate highways, meaning an exit is numbered based on what milepost it falls after. This is by far better than sequential numbering (1, 2, 3,...), which is employed by several eastern states. If a freeway isn't an Interstate highway, it doesn't have any exit numbers (E-470 is the only exception to this).


Structure Number Signs

One for the FAQ file: What are the small white signs with non-sensical numbers and letters at bridges? They are CDOT structure numbers, and are the internal system CDOT uses to catalog and track structures on the state highway system. (Local governments have their own systems.) CDOT assigns a structure number to any bridge, overpass, pedestrian overpass, tunnel, retaining wall, overhead sign structure, or large box culvert on a state highway. The structure number takes the form A-11-AA. The signs identifying the structure number are usually placed off the right edge of pavement adjacent to the structure pier or abutment. Starting in the late '90s, the standard was amended so that the sign also includes the milepost of the structure.

As to determining what number a structure gets, CDOT Staff Bridge assigns them based on a two-part system. The first letter-number sequence, A-11 comes from the location of the structure in the state, based on the grid on the sides of the CDOT state map. A-1 is the northwest corner, continuing east across A-2, A-3, etc. to A-28 in the northeast corner, and then down through the rest of the grid eventually ending at P-28 in the southeast corner of the state. The final letters come from starting at A in that grid area and counting up sequentially as each structure is built. Once A is reached it goes to AB, AC, etc. and would eventually top out at ZZ. The photo on the right, F-16-KD, happens to be US 85 (Santa Fe Drive) over Little Creek in central Littleton.


The National Highway System in Colorado

The act that repealed the national 55 speed limit was actually the National Highway System Designation Act of 1995. This act scrapped the old Federal Aid Primary/Federal Aid Secondary systems, in favor of a more coherent system of major intra- and interstate highways that the states submit to the Federal Highway Administration. Rather than giving money to the states to keep up most cowpaths under the FAP/FAS system, the NHS is committed to upkeeping the most important highways. Highways in the NHS get federal financing so the states can keep them in good condition. Interstates are by default part of the NHS.



Last updated 25 May 2015