Turn a dial, click a number, or use the arrow keys. Ramps go up to two either side, and only up to 60 km/h, as on real roads.
Adjust this junction
Use this junction’s collision record
Enter the average a year from RSA or Garda records. Leave at zero to use the indicative PAG average.
Enter the average crashes a year from the state crash database (3 to 7 years). US DOT discourages average crash rates, so crashes count only once entered.
Your settings, not the published standard case
At this traffic the junction is over capacity. Signal delay is shown at the capacity limit, so real waste would be higher.
What is counted at this junction
Every vehicle passing pays some of these. A free-flow junction removes all of them.
| Event | What happens | Who it applies to | Counted here |
|---|
Each event is net of the fuel a vehicle would burn anyway, cruising the same distance at the speed limit.
The same junction at every speed limit
The selected speed limit is highlighted. Faster roads carry more energy into every stop, so the Momentum Tax rises with speed. Speed ramps are left out above 60 km/h, where they are not used on real roads.
How it is calculated
For each vehicle class (cars, vans, rigid lorries and articulated lorries, at average operating masses) the model works out the energy needed to get back up to speed after every slowdown, the fuel burned waiting, and subtracts what the vehicle would have used anyway. Stop share and waiting time at signalised junctions come from the signal timing, using Webster’s method, the standard traffic engineering formula. Energy is counted well to wheel, including the energy used to produce and deliver the fuel.
What is PAG?
The Project Appraisal Guidelines (PAG) are Transport Infrastructure Ireland’s rules for valuing the costs and benefits of road schemes. Unit 6.11 sets the official values every Irish scheme must use: what an hour of travel time is worth, the shadow price of a tonne of carbon, and the cost to society of a collision by severity. They are set in 2016 prices and grown each year in line with the economy; this calculator uses 2026 values. Using PAG means the Momentum Tax is valued the way a council, TII or the Department of Transport would value it when deciding whether to fund a scheme.
| Item | Value used | Source |
|---|---|---|
| Value of travel time | about €15.70 per person-hour, 1.4 people per vehicle | PAG Unit 6.11, Table 6.11.9, blended across work, commuting and other trips (trip mix assumed) |
| Shadow price of carbon | €346 per tonne (2026) | PAG Unit 6.11, Table 6.11.6 |
| Collisions | Indicative PAG average for the speed limit, or the site record if entered; 75% assumed removed by a free-flow junction | PAG Unit 6.11, Tables 6.11.20, 6.11.22 and 6.11.23 |
| Fuel supply energy | 19% added for extraction, refining and delivery | Consistent with the EU JEC Well-to-Wheels study |
| Signal timing | 90-second cycle, two stages; a 20-second pedestrian stage for the all-red type | Assumption; replace with the council timing plan for a real site |
| Ramped crossing | Two ramps, 30% of vehicles stop, 15-second wait, 15 km/h over each ramp | Assumption |
| Extra ramps | Between ramps on the same side, traffic regains the same speed it reaches after the first ramp | Assumption, extending the workbook to up to four ramps |
| Traffic mix | 73% cars, 12% vans, 7% rigid and 8% articulated lorries at average operating masses | Workbook defaults; the slider changes the lorry share |
US DOT values
In the USA the Momentum Tax is valued with the US Department of Transportation’s Benefit-Cost Analysis Guidance for discretionary grant programs (December 2025, for FY2026 applications, in 2024 dollars), the values a state DOT or city uses when applying for federal funding. Carbon is shown in tons but not in dollars, because current US DOT guidance no longer monetizes carbon dioxide.
| Item | Value used | Source |
|---|---|---|
| Value of travel time | $21.80 per person-hour, 1.52 people per vehicle | US DOT BCA Guidance, Dec 2025, Table A-2; occupancy from the May 2025 edition |
| Crash costs | $15.37m per fatal crash, $342,400 per injury crash, $9,700 per property-damage-only crash; counted only from the crash record you enter; 75% assumed removed | US DOT BCA Guidance, Dec 2025, Table A-1 |
| Carbon | Tons only, not monetized | US DOT guidance under Executive Order 14154 and OMB M-25-27 |
| Fuel prices | Gasoline $4.33 a gallon for cars, SUVs, pickups and vans; diesel $6.18 a gallon for trucks | EIA Gasoline and Diesel Fuel Update, US averages for 12 October 2026, all taxes included |
| Vehicle masses | Cars and SUVs 2,000 kg and pickups and vans 2,600 kg (estimates); tractor-trailers 24.5 t average (80,000 lb is the legal maximum, not the average); single-unit trucks 15.5 t (placeholder) | Oak Ridge National Laboratory weigh-in-motion example (ORNL/TM-2019/1385) for tractor-trailers; others to be confirmed |
| Traffic mix | 70% cars and SUVs, 22% pickups and vans, 3% single-unit and 5% tractor-trailers | Assumption for a suburban arterial, informed by FHWA national counts |
| Speed humps | Recovery speeds between humps at 25 and 35 mph interpolated from the Irish model | Assumption |
| Signal timing | Same 90-second, two-phase plan as the Irish model; right turn on red not yet modelled | Assumption; replace with the agency’s timing plan |