// civil transportation

Civil Transportation Engineering Suite

Planning and preliminary-design calculators for roadway geometry, pavement design, intersection operations, sight distance, and trip generation.

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TOOLS07

UNIT SYSTEMSUS · SI

STATELOCAL

STATUSPRELIMINARY

02 · Calculator suite

Seven planning tools

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Stopping Sight Distance
Horizontal Curve
Vertical Curve
Pavement Structural Number
Intersection LOS / Capacity
Intersection Sight Triangles
Trip Generation

Stopping Sight Distance

Direct kinematic estimate using reaction distance plus grade-adjusted braking distance.

Enter valid inputs and select Calculate. No result is shown until validation passes.

Method and references

SSD = vt_r + v² / (2a_effective)

Canonical calculation uses SI kinematics. Positive upgrade adds gG to braking deceleration; downgrade subtracts it. The rounded value is the unrounded result rounded upward to one displayed length unit, not a tabulated agency design value.

FHWA-RD-02-045 (2003), equation 3.5.1, and dimensional kinematics. Verify reaction time, wet-pavement braking criteria, grade convention, and agency rounding.

Horizontal Curve Radius and Superelevation

Solve the point-mass relationship for radius, superelevation, or side-friction demand without an embedded friction table.

Enter valid inputs and select Calculate.

Method and references

v² / (gR) = e + f

Superelevation entered as percent is converted to a decimal ratio. US customary equivalent: R ≈ V² / [15(e + f)].

FHWA-HRT-17-098 (2018), point-mass model. Final selection must address agency superelevation policy, runoff, transitions, drainage, climate, urban context, and side-friction criteria.

Vertical Curve Length — K-Value Method

Calculate preliminary curve length from a user-entered K-value and algebraic grade difference.

Authorized lookup data not bundled · K required

Supply a K-value from the governing reference, then calculate.

Method and references

A = |g₂ − g₁| · L = KA

A uses percentage points; K uses length per percent. No AASHTO K-value table is generated or approximated.

AASHTO-based preliminary relation. The user must select K and any minimum length from an authorized, applicable governing edition and agency policy.

Pavement Structural Number — AASHTO 1993

Bounded bisection solution of the implicit flexible-pavement equation.

Z_R required · reliability mapping not bundled

Enter valid equation inputs and calculate.

Method and references

log₁₀(W₁₈) = ZR·Sₒ + 9.36log₁₀(SN+1) − 0.20 + log₁₀(ΔPSI/2.7) / [0.40 + 1094/(SN+1)^5.19] + 2.32log₁₀(MR) − 8.07

Bisection searches SN ∈ [0, user-entered maximum], requires a bracket, retains full precision, and reports iterations and residual.

AASHTO Guide for Design of Pavement Structures (1993); equation reproduced in FHWA NHI-05-037 (2006), chapter 3. Layer coefficients, drainage coefficients, constructability, and agency minimum sections remain separate design work.

Intersection LOS / Capacity Estimator

Simplified directional screen using user-entered capacities and control delays. It does not calculate formal HCM delay.

HCM-aligned planning estimate · not formal operational analysis

Supply directional capacity and average control delay assumptions, then calculate.

Method and references

v/c = hourly adjusted directional demand / user-entered directional capacity

LOS is classified only from user-entered control delay using control-specific threshold sets. The lane note documents geometry but does not calculate capacity.

Signalized thresholds: FHWA-HOP-08-024 (2008), table 3-3. This screen omits timing, progression, lane utilization, pedestrians, heavy vehicles, queues, turns, calibration, and formal HCM movement analysis.

Intersection Sight Triangles — AASHTO Case-Based

Calculate the major-road leg from speed and a user-supplied time gap; report the minor-road eye setback as leg a.

Time gap required · no proprietary table bundled

Supply a governing time-gap criterion, then calculate.

Method and references

b = 1.47 V_majort_g (US) · b = (V/3.6)t_g (SI)

Leg a is the entered eye setback to the near edge. Leg b is measured along the major-road traveled way. No lane-count or grade time-gap adjustment is invented.

AASHTO-based Case B departure relationship using a user-supplied criterion. Verify horizontal and vertical obstructions, eye/object heights, curvature, skew, grades, and adopted jurisdictional standards.

Trip Generation Estimator — ITE-Based

Apply a user-supplied or otherwise authorized average rate. No proprietary ITE rates are embedded.

Reference data required · custom land use only

Supply an authorized rate and source disclosure, then calculate.

Method and references

T = R X

The independent-variable quantity must already be normalized to the rate unit. User-entered pass-by, diverted-link, and internal-capture reductions are applied sequentially and shown separately.

No ITE-published rates or equations are included. Verify the authorized dataset, local validation, mixed-use effects, multimodal reductions, pass-by treatment, and jurisdictional policy.

Disclaimer

Preliminary engineering tool. Results are for planning and preliminary evaluation only and must be independently verified against governing-agency requirements and the applicable editions of AASHTO, HCM, ITE, and other controlling references. Not for final design or construction without independent professional review.