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Preliminary tool · v1.0

// 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 · Geometric Design

Sight distance & roadway alignment

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 = vtr + v2 / (2aeffective)

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. Select and verify K independently for the project design speed and governing standard.

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.

03 · Pavement Design

Flexible pavement structure

Pavement Structural Number — AASHTO 1993

Bounded bisection solution of the implicit flexible-pavement equation. ZR is derived from the selected reliability.

Reliability required · ZR calculated

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

ZR is the lower-tail standard-normal quantile corresponding to 1 − R. 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.

04 · Traffic Operations

Intersection capacity & sight triangles

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
Approach / lane noteDemand (selected basis)Capacity (veh/h)Delay (s/veh)

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

Method and references
v = V/PHF for a 60-minute volume   ·   v = 4V15 for a peak 15-minute count   ·   v/c = v / user-entered capacity

PHF is the hourly volume divided by four times the peak 15-minute count. A peak 15-minute count therefore already represents the peak flow rate after multiplication by four and is not divided by PHF again. LOS is classified only from user-entered control delay using control-specific threshold sets.

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 Vmajortg (US)   ·   b = (V/3.6)tg (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.

05 · Trip Generation

Travel-demand estimate

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. Reductions are applied in this order: internal capture, pass-by, then diverted-link. Driveway entering/exiting trips include pass-by and diverted-link traffic after internal capture; new external roadway trips exclude those reductions.

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.

06 · Disclaimer

Engineering reference tool only. Calculations are provided for preliminary engineering evaluation and must be independently verified by a licensed professional engineer against the applicable editions of governing standards, references, and agency requirements. Use of this software does not replace applicable engineering judgment, governing codes, manufacturer guidance, or agency standards.