New project

Start from a map

Aerial imagery with the scale set from the latitude, street names on top if you want them. Nothing to calibrate.

Or from an image

A screenshot, survey or site plan. You will calibrate the scale by clicking two points a known distance apart.

How it works

Pick a vehicle, draw the path its front axle should follow (or, when backing in, the path the rear of the trailer should follow), and the app drags the rest of the vehicle along behind. The orange envelope is everything the bodies sweep over; the red lines are the rear wheel tracks, which cut furthest inside a turn.

Tools

• Path (P) — click to add points, drag to move them, right-click to remove one.
• Curb (C), Building (B), Post (O) — mark what must be cleared. Each reports its closest approach, and turns red when hit.
• Select (V) — move points and whole obstacles. Delete removes the selection.
• Measure (M) — two clicks show the distance between them.
• Pan (H) — or hold Space and drag, or drag with the middle button. Scroll to zoom.
• Undo / Redo — Ctrl+Z, Ctrl+Shift+Z. . plays and pauses, [ and ] step.

Reading the numbers

• Steering needed against the vehicle's lock: past it, the path is red and the vehicle cannot follow it.
• Articulation is the angle at the hitch; past 75° the model calls it a jackknife.
• Off-tracking is how far the rear axle strays from the front axle's track through the turn.

Where the vehicles come from

The AASHTO entries are the design vehicles from the Green Book, which is what traffic engineers use for the same check. The typical entries are representative; customize a copy to match a specific unit. The model is the standard tractrix (rear axle follows the point ahead of it) used by swept-path software; it does not account for tire scrub, superelevation or speed.

Privacy

Projects, custom vehicles and images stay in this browser. Map tiles are fetched from Esri, USGS or OpenStreetMap and address searches go to OpenStreetMap's Nominatim; those requests carry the location you look at and nothing else. OpenStreetMap's tile servers require the browser's Referer header and refuse requests without it, so their tiles will not load from a file:// copy of the app or with an extension that strips referers; the aerial providers do not care.