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Acceleration and Deceleration Lane Calculator

Explore speed-change lane lengths using the original average-running-speed model and grade factors.

by Shahid Pervaiz: pervaiz.shahid@gmail.com
Not saved to a file yet 📄 See Sample Report
Reference: AASHTO 2001 Green Book §10.9.6 Tables: 10-4 (Acceleration) · 10-5 (Grade) · 10-6 (Deceleration)
Deceleration Length — AASHTO 2001 · Table 10-6
Highway
Design Speed (kph)
Average Running Speed (kph) 85
Exit Curve
Design Speed (kph)
Average Running Speed (kph) 35
Grade Adjustment — AASHTO Table 10-5
Highway Grade
Grade Adjustment Factor 1.00
− grade = downgrade (harder to stop; longer lane required).
+ grade = upgrade — no reduction taken per AASHTO conservatism.
Deceleration Length (m) 145
Grade-adjusted length (m) 145
Computed Values
Highway ARS85 kph
Exit ARS35 kph
ARS Differential50 kph
Base Length145 m
Grade Factor1.00
Adjusted Length145 m

Based on AASHTO 2001 formula using Average Running Speeds (ARS):
L = (ARSH² − ARSE²) / 41.47  [adec = 1.6 m/s²], rounded to nearest 5 m.
Verified: VH=100, Vexit=40 → ARS 85 vs 35 → L = 145 m ✓

Calculated deceleration lengths — approximation (m)

Highway Design Speed shown across top; Exit Curve Design Speed down left. highlighted = current selection.

Average Running Speed Reference — AASHTO 2001
Design Speed (kph) 2030405060708090100110120130
Avg Running Speed (kph) 2028354754627077859197102

ARS values from AASHTO 2001 Exhibit 3-1. The speed-change lane length is based on the difference between the Average Running Speeds of the highway and the entry/exit curve — not the posted design speeds.

Grade Adjustment Factors — AASHTO 2001 Table 10-5

Deceleration: Negative grade (downgrade) opposes braking → factor > 1 (longer lane required). Positive grade (upgrade) — AASHTO takes no credit; factor = 1.00 (no reduction).
Acceleration: Positive grade (upgrade) opposes acceleration → factor > 1 (longer lane required). Negative grade (downgrade) — AASHTO takes no credit; factor = 1.00 (no reduction).

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Method & practical use

Understand the result.

Explore speed-change lane lengths using the original average-running-speed model and grade factors.

How to use this tool

  1. Select the geometry or design case and confirm the displayed units.
  2. Replace sample inputs with the project values, then calculate or review the live result.
  3. Check the method, assumptions and output; save or print the calculation with its input record.

Units & method

Speed km/h; length m; grade %.

The implementation uses L = (ARS_H² − ARS_E²)/(25.92a), rounded to 5 m, with a = 1.6 m/s² for deceleration and 0.8 m/s² for acceleration. The source labels its speed/grade inputs AASHTO 2001. This model is an approximation, not a verified reproduction of Tables 10-4 to 10-6; DMRB is not implemented.

Worked examples

Illustrative inputs for checking the method; these are not project records.

100 km/h highway and 40 km/h ramp

Using average running speeds 85 and 35 km/h on level ground, the implemented constant-acceleration model gives 145 m for deceleration and 290 m for acceleration after rounding. These are model checks, not published table certification.

80 km/h highway and 40 km/h ramp

Using average running speeds 70 and 35 km/h on level ground, the implemented constant-acceleration model gives 90 m for deceleration and 175 m for acceleration after rounding. These are model checks, not published table certification.

Frequently asked questions

What does this tool calculate or track?

Explore speed-change lane lengths using the original average-running-speed model and grade factors.

Which units and assumptions should I use?

Speed km/h; length m; grade %. The implementation uses L = (ARS_H² − ARS_E²)/(25.92a), rounded to 5 m, with a = 1.6 m/s² for deceleration and 0.8 m/s² for acceleration. The source labels its speed/grade inputs AASHTO 2001. This model is an approximation, not a verified reproduction of Tables 10-4 to 10-6; DMRB is not implemented.

Can I save or share the result?

Use the save, export and print controls shown in this workspace. Where CSV export is available, the exported data can be opened in a spreadsheet. Browser print can save a PDF.

Continue your workflow

How to use the Acceleration and Deceleration Lane Length Calculator

Everything runs in your browser — nothing is uploaded. If you are new to the tool, follow these steps in order.

1

Enter your inputs and read the results

Choose a calculation with the two buttons at the top: ⬇ Deceleration Length or ⬆ Acceleration Length. Results update as you type, so there is no Compute button to press.

  • Project / road name and Prepared by — shown on the printout and report, and used to name saved files.
  • Design speeds — the highway design speed and the exit or entry curve design speed; average running speeds are taken from AASHTO.
  • Highway grade — the grade adjustment factor is applied automatically (downgrade for deceleration, upgrade for acceleration).
  • Computed Values and AASHTO tables — the lane length, with the AASHTO tables shown and the row and column used highlighted.
2

Save your project and open it later

💾 Save Project (.json) saves every input on the page in one .json project file. 📁 Load Project opens that file again, on any computer.

The note beside the Save button tells you whether you have unsaved changes or when you last saved. If you try to close or leave the page with unsaved changes, the browser asks you to confirm first.

Use the project file for backups and for sharing with colleagues. Don't edit it by hand.

This tool does not autosave. Save your project before closing the page.

3

Print, PDF and report

  • 📄 Generate Report opens the full design report for both calculations in a new tab, with its own Print / Save as PDF button. If nothing opens, allow pop-ups for this site. To see a report the tool makes from its sample design (4 pages, PDF), press 📄 See Sample Report beside How to use.
4

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