This calculator is different from the others, because it never gives a capacity that requires drivers to violate safe following distances.
Sets which units of measure are used for the input values of speed (spd) and length (len). Four settings are possible:
Note: Changing this setting does not change any numbers already entered as speeds or distances to converted values. Instead, the entered values are now changed to be in the new measurements.
Sets the kind of intersection the capacity is calculated for.
Note: The effects of each setting are covered separately for each variable.
Calculates the values of capacity, lane capacity, and headway.
Clears all values in the grid to zero.
Enter the number of lanes on the approach for each type of lane. Note that there can be only one shared lane of each kind.
Enter the width of a lane for each type of lane. Uses the "wid" setting in Measurement to select the units.
Enter the speed for each type of lane. Uses the "spd" setting in Measurement to select the units.
Enter a value between 0 and 1 denoting the portion of traffic in the selected lane that consists of heavy vehicles. For example, 0.25 denotes that 1/4 of the traffic on the lane is truck traffic.
Enter the portion of time the signal is green for the selected lane(s). For example, a value of .6 means the signal is green 60% of the time. Used only when the intersection type is Signal.
Number of vehicles moving in conflict with each lane type:
Check if parking is allowed in a parking lane to the immediate left of the leftmost active lane in the grid. Used only for one-way streets and streets allowing parking next to the median.
Check if parking is allowed in a parking lane to the right of the rightmost active lane in the grid.
For lanes with more than one movement, enter the portion of traffic expecting to make turns.
Check the box if the approach is one way with no oncoming traffic conflicting with left turns.
Gives the capacity in vehicles per hour for the entire group of lanes in the column.
The total at the right is the total for the entire approach.
Gives the capacity in vehicles per hour for each lane in the group of lanes in the column.
The average at the right is the average traffic per lane for the entire approach.
Note that if the parking checkbox is checked, the 500 veh/hr would be removed from the right lane, but this calculation spreads it among more than one lane in the group.
Gives the spacing between vehicles in seconds per vehicle as an average of the lanes in the group.
The average at the right is the average headway over the entire approach.
Notice: If a small number of lanes feeds a much larger number of lanes at the intersection, do a second calculation for just the small number of lanes, using only the thru lane column, to find out if the road capacity is less than the intersection approach capacity.