General Lane Closure Impact Analysis Corridors 2020 Backbone Routes NC Region | NE Region | NW Region | SE Region | SW Region

Welcome The General Lane Closure Analysis is designed to help manage the impacts of temporary lane closures on Wisconsin’s freeways and expressways. It is intended primarily for maintenance projects and small construction projects, where a more detailed analysis is not feasible due to time or budget constraints. Information on how to use the analysis can be found here. The results are based on a simplified analysis with the following assumptions:

1. Backbone Routes. To use this analysis, the project must be located on a divided highway that is part of the Corridors 2020 Backbone system, which includes all Interstates and most other high speed 4-lane and 6-lane divided highways. Routes with Annual Average Daily Traffic (AADT) volumes less than 25,000 were only analyzed at locations where Automatic Traffic Recorder (ATR) data was available.
2. Limited Duration. The duration of the project should of limited duration (generally less than 14 days of construction) and should be similar to one of the three scenarios that were analyzed: continuous 24-hour closure, mid-day closure, or night-time closure.
3. Diversion Route Available. When serious congestion occurs, it is normal for some traffic to divert to an alternate route. This analysis includes an hour-by-hour estimate of the number of vehicles that are expected to divert. The capacity and suitability of the diversion route needs to be checked separately, especially if the congestion level is high (more than 4 hours). Unusually high diversion volumes are marked with a + (plus sign) to indicate the potential for severe operational problems on diversion route(s).
4. No Crossovers. The lanes that remain open must be on the normal side of the divided highway—the analysis assumes that traffic is not being "crossed over" to run "contraflow" on the opposite side of the highway median.
5. Relatively Low Work Zone Capacity. A relatively conservative work zone capacity of 1500 vehicles per hour per lane was assumed in this analysis. This corresponds to short-term closures (using cones or barrels) and moderate to high truck volumes.
6. No Demand Management. The analysis assumes that special demand management measures will not be used during construction. (Some typical demand management measures are: public information campaigns that encourage drivers to change their travel time or use a different route, adding extra commuter bus service, and prohibiting trucks in the work zone).

If the assumptions listed above do not apply to your project, contact the Bureau of Highway Operations for information about running a customized project-level analysis.

Project Level Analysis is strongly recommended in the following situations: closure of two or more consecutive freeway segments, closure during time periods that differ from the pre-selected ones, closure occuring during unusually high traffic demand (such as a major sports event), closure that occurs while work is also being done on alternate routes, closure that affects both travel directions simultaneously (such as a crossover), projects that restrict lane capacity without closing a lane (such as sharp lateral shifts or very narrow lanes), projects that involve complicated construction staging, long-term work (more than about 2 weeks), projects that impact multiple routes (such as interchange reconstruction), and projects that will use special demand management measures.

How to Use the Analysis Results

1. To begin, select a Region from the menu at the top of this page:
   

   Next, select a highway corridor:
   
   

2. A location map can be obtained by clicking on the segment title:
   
   

   In this case, the Main Route (freeway) is shown in purple, and the Diversion Route (detour or alternate route) is shown in red. In urban areas where a grid of alternate routes exist, the Diversion Route is not identified specifically.
   
   

3. Colors identify the number of congested hours associated with each closure scenario:

   

   
   The legend is as follows:
   
   "Congestion" means delay increases of more that 15 minutes compared to the travel time under normal traffic conditions (without construction).

   Example:

   On a particular highway, between 7:00 AM and 8:00 AM the travel time from A to B is normally 10 minutes. Because of lane closures during construction, at that time of day the travel time from A to B is expected to increase to 25 minutes. This is 15 minutes of extra delay, and the 7-8 AM hour would be flagged as a "congested" hour.
   
   

4. To see the details of the analysis, select the appropriate direction, month, and closure duration and then click the digit representing the number of congested hours:
   
   

   
   This will bring up a PDF file that shows the detailed analysis results. The first page shows the results in a tabular format, followed by a set of 4 graphs:
   
   

   

5. The demand graph shows how the normal traffic volume on the route varies during the day:
   
   

   Note: A blue horizontal line is shown at 1500 vehicles per hour, which for the purposes of this analysis is assumed to be the capacity of a one-lane freeway work zone. This is a fairly conservative assumption. Under non-construction conditions freeway lanes have a capacity of about 2200 vehicles per hour.

   The corresponding values are shown in the table. “Main” means the main highway (in this case I-39) and “Diversion” means the alternate route (in this case Business US 51):
   
   

6. If the traffic demand exceeds the capacity, the number of queued vehicles is shown on the Queue length graph:
   
   

   The corresponding values are also shown in tablular format:
   
   

   TIP: To estimate the queue length in miles, divide the number of queued vehicles by the "jam density" (typically 150 vehicles per mile) and divide by the number of lanes available upstream of the lane closure: Queue Length ≈ Number of Queued Vehicles ÷ Jam Density ÷ Number of Upstream Open Lanes For example, if there is a 679 vehicle queue with two lanes open upstream of the work zone, the queue length is approximately: 679 veh ÷ 150 vehicles/mile ÷ 2 lanes ≈ 2.26 miles

   
   
7. In severe congestion, some vehicles may divert from the freeway and use an alterate route. This analysis assumes that when that happens, the travel time on the Main Route and Diversion Route will equalize. The increase in delay (compared to the normal travel time) is graphed on the Delay Chart:

   

   
   This information is also presented in tabular format. Delays greater than 10 minutes are highlighted in yellow and delays over 15 minutes are highlighted in red.
   

8. The speeds in the work zone are compared with the normal speeds. In addition to the tabular results, the graph provides a quick hour-by-hour comparison of the work zone speeds and the normal speeds:
   
   
9. In urban areas it is often difficult to identify a single diversion route. In these cases, it is assumed that drivers will tolerate about 15 minutes of delay before some start using a variety of alternative routes. This is called the "maximum queue delay" analysis method. The "Diverted" column shows how many vehicles must avoid the freeway in order for the delay to be limited to 15 minutes:
   
   

   Pale yellow shading appears as a warning if the number of diverted vehicles exceeds 50% of the total freeway demand. This could be a troublesome situation, since the local streets may not have enough capacity to handle all of the diverted vehicles.
   
   

10. For Mid-Day and Night-Time closures, the word "OFF" will appear in the Site Capacity column to indentify hours when the construction is "off" and all lanes are assumed to be open to traffic:
    
    

11. When freeway traffic diverts to an alternate route built to lower standards, the chances of a crash increase. This effect is shown near the lower right corner of the results table. It compares the expected number of Personal Injury Accidents per day, with and without construction works:
    
    
12. It is often said that time is money. The effects that traffic delays have on road users can be converted to a dollar figure to help guide decisions about whether to spend money on a more expensive work zone traffic control strategy (or construction method) such as night work. The economic impacts of the lane closure are shown at the bottom right corner of the results table. These road user costs include delay, extra fuel and vehicle wear resulting from driving on a diversion route, and costs associated with increased risk of traffic accidents.
    

Created 14-Apr-09
WisDOT Bureau of Highway Operations