A vehicle tracking BMP is a rock (stone, gravel) pad, shaker rack, wheel washer, or other BMP designed to remove soil and mud from vehicles leaving the work zone and entering offsite areas, such as public roadways and public or private parking lots.
Vehicles leaving construction sites track sediment onto adjoining roadways. This sediment can create safety hazards and contribute significantly to sediment pollution in waterways. The purpose of a vehicle tracking BMP is to prevent soil and mud on work vehicles from being carried offsite and deposited on public roads, parking lots, and other areas. Temporary site entrances/exits are used during the construction period, prior to the time when roadways, parking lots, and other areas are either paved or stabilized. Vehicle tracking BMPs limit the amount of sediment and other pollutants leaving the construction site and reduces discharge of sediment and pollutants to surface waters. Pollutant removal is primarily accomplished through the removal of soil and mud from construction equipment, including nutrients and heavy metals that are associated with sediment (see section on Effectiveness).
Vehicle tracking BMPs are installed at all construction sites where there is a risk of mud and soil clinging to vehicles leaving the site.
Vehicle tracking BMPs are appropriate during the construction period for all sites with vehicles passing through disturbed areas prior to entering public roadways or other offsite areas.
The 2018 Construction Stormwater permit states: In any areas of the site where final vegetative stabilization will occur, permittees must restrict vehicle and equipment use to minimize soil compaction. Permittees must install a vehicle tracking BMP to minimize the track out of sediment from the construction site or onto paved roads within the site. Permittees must use street sweeping if vehicle tracking BMPs are not adequate to prevent sediment tracking onto the street. In any areas of the site where final vegetative stabilization will occur, permittees must restrict vehicle and equipment use to minimize soil compaction. Permittees must inspect construction site vehicle exit locations, streets and curb and gutter systems within and adjacent to the project for sedimentation from erosion or tracked sediment from vehicles. Permittees must remove sediment from all paved surfaces within one (1) calendar day of discovery or, if applicable, within a shorter time to avoid a safety hazard to users of public streets.
If permittees wash the exterior of vehicles or equipment on the project site, washing must be limited to a defined area of the site. Runoff from the washing area must be contained in a sediment basin or other similarly effective controls and waste from the washing activity must be properly disposed of. Permittees must properly use and store soaps, detergents, or solvents. No engine degreasing is allowed on site.
Properly installed, and maintained vehicle tracking BMPs are effective at removing mud and soil from vehicles leaving the site. The overall effectiveness can range from low (less than 30 percent soil removal) to moderate (30 to 60 percent removal) for rock pads and shaker racks, depending on the design, installation, frequency of use, and maintenance. For example, effectiveness of rock pads will decrease as rock voids become clogged with soil and mud. To prevent this, the rock must be periodically topdressed with additional rock, replaced, or the length of the pad increased. Properly installed and operated wheel washer units are effective at removing more than 75 percent of sediment in nearly all applications. The following table summarizes expected performance for an array of typical water quantity and quality target constituents for temporary vehicle tracking BMPs.
Expected performance for temporary vehicle tracking BMPs.
Link to this table
|Flow attenuation||Little or no design benefit|
|Runoff volume reduction||Little or no design benefit|
|Erosion prevention||Little or no design benefit|
|Sediment control||Primary design benefit|
|Nutrient loading||Secondary design benefit|
|Total suspended solids||Primary design benefit|
|Total phosphorus||Secondary design benefit|
|Heavy metals||Secondary design benefit|
|Floatables||Little or no design benefit|
|Oil and grease||Little or no design benefit|
When planning a vehicle tracking BMP, the following guidelines should be followed.
In this section, design and construction guidance is provided for three designs:
All three designs include the planning and siting information discussed above, along with considerations for managing sediment that accumulates at the site. For most applications, the vehicle tracking BMP area can be graded to facilitate drainage toward a stabilized swale or ditch which empties into a treatment area. This treatment area can include a sediment trap, a curved section of silt fence (i.e., with the ends turned uphill to prevent bypasses), a sediment pond, or other sediment removal device. Additionally, a pipe, culvert, or water bar can be constructed as part of the BMP if needed to prevent surface water and runoff from flowing across the entrance and out onto paved roadways.
Rock/stone pads remove material from vehicle tires through physical scraping action. Additionally, vehicle tracking pads can be installed to provide a barrier and keep the truck wheels from coming in contact with wet, sticky underlying soils. The amount of construction traffic and frequency of use should be considered when designing a vehicle tracking pad. Specific design requirements include the following:
Shaker racks – also called exit grids, rumble strips, rumble racks, rumble plates, etc. – remove material from vehicle tires through bouncing and shaking action. These are appropriate when the rock pad alone is not sufficient to remove sediment from tires. Wheel washers (see below) may be necessary if rock pads and shaker racks are ineffective. Where used, shaker racks must be long enough and create enough rumble or shake to dislodge mud, soil, and rock. They can be fabricated from concrete or metal (i.e., similar to cattle guards), or acquired from construction site stormwater compliance vendors. Specific design requirements include the following:
In many cases, the action of tires moving over the rock pad may not adequately remove sediment, and a wash rack may be required. Wheel washer systems – also called wash racks – use pressure-sprayed water to remove mud, soil, and rock from vehicles exiting the site. They can be fabricated from piping, hoses, driveway racks (e.g., concrete and metal cattle guards), and other materials, or acquired from construction site stormwater compliance vendors. Designs range from pipe units that can be hung from Jersey wall sections to wash stations that include elevated driveways above sediment trapping basins. Specific design requirements include:
A wash rack installed on the rock pad may make washing more convenient and effective. The wash rack would consist of a heavy grating over a lowered area. The grating may be a prefabricated rack, such as a cattle guard, or it may be constructed on site of structural steel. The wash rack must be strong enough to support the vehicles that will cross it.
MnDOT Standard Plan 5-297.405 provides standard detail for “Construction Exits” (effective date: 8/6/2014). BMPs covered include “Slash Mulch, Crushed Rock, or Sheet Pad Construction Exit” and “Rumble Pad Construction Exit” (See page 31, Standard Plan 5-297.405, 5 of 7).
MnDOT Specification 2573.3.K (Construction Exit Controls) provides guidance for exit type selection and use, and ranks exit controls from lowest to highest protection. Specification 3882 (Mulch Material) may also be applicable, depending on the exit type selected (See page 507).
Vehicle tracking BMPs require continuous monitoring, especially during and after rain events and during snowmelt, due to the risks posed by mud, soil, and other debris on roadways – especially high speed urban and rural highways. Specific inspection requirements include the following.
If site inspection(s) reveal concerns, maintenance will be necessary. Maintenance of vehicle tracking BMPs includes the following:
Maintenance of wheel washers/wash racks includes the following:
Cold weather considerations include the following:
The following estimated BMP cost is based on MnDOT data summarizing average bid prices for awarded projects in 2014.
Except where more stringent requirements are presented in this guidance, vehicle tracking BMPs shall comply with MnDOT and other state requirements. Primary design references include:
The following is a list of additional resources that are not specific to Minnesota: