What is a variable message sign (VMS)? A plain-English guide
4 min read
A variable message sign, or VMS, is any electronic sign whose message can be changed. That covers the amber message boards you pass at roadworks, the overhead signs on motorways, and the full-colour LED screens on trailers at events and car yards. From a distance they look alike, but they're built for different jobs and follow different rules.
The main types
Fixed road VMS
These are permanent signs on gantries or poles over and beside major roads. Road authorities use them for travel times, incidents, lane closures and safety messages, and they own and run them.
Portable traffic VMS
These are the trailer-mounted message boards used at roadworks, crashes and events to warn and direct traffic. They usually show text and simple symbols in amber or white on black, sized to be read at speed. Most run on solar panels and batteries so they can sit on a roadside for weeks.
Full-colour LED screen trailers
These carry a full-colour LED screen, like a billboard on wheels. They show photos, logos and video, and they're used for advertising, events, sport, promotions and site information. Our LED trailers are in this group.
The Australian standards
Signs used for traffic control on public roads have to meet technical standards:
- AS 4852.2 sets minimum performance requirements for portable variable message signs, the kind mounted on relocatable trailers.
- AS 1742.3 covers traffic control at roadworks, including where signs go and how they fit into a traffic management plan.
Road authorities can add their own requirements on top, and some keep lists of accepted products. If a sign will be part of traffic control on a public road, check with the road authority or your traffic management company before you choose one.
Which kind do you need?
| Job | Better fit |
|---|---|
| Warning and directing traffic at roadworks on a public road | Portable traffic VMS that meets AS 4852.2 |
| Advertising a sale or a grand opening | Full-colour LED screen trailer |
| Event information, sponsors and schedules on private grounds | Full-colour LED screen trailer |
| Safety messages and inductions on a private work site | Either, depending on the content |
| Car park and venue directions on private land | Either, depending on the content |
The key question is whether the sign controls traffic on a public road. If it does, it needs to be a compliant traffic VMS used under a traffic management plan. If it's for promotion or information on private land, a full-colour screen gets far more attention and can show your branding, photos and video.
What to look for in a full-colour LED trailer
- Screen size and pixel pitch. Match them to how far away people will be. See our pixel pitch guide.
- Brightness. Outdoor LED needs enough brightness for daylight, with dimming for the evening. Our brightness guide explains why.
- Power. Our trailers run on mains power, so plan for a power point nearby. If your site has no power at all, we can put you in touch with one of our solar LED trailer partners.
- Height. A raised screen clears parked cars and crowds.
- Content control. Check how you'll load and schedule content.
- Towing. Check the trailer's weight against your vehicle's towing capacity.
Common questions
What does VMS stand for?
Variable message sign: an electronic sign whose message can be changed, either remotely or on site.
Can a full-colour LED trailer be used for roadworks traffic control?
Only if it meets the requirements for traffic control on that road, including AS 4852.2 and the road authority's own rules. For advertising and information on private land, a full-colour LED trailer is the usual choice.
Do VMS trailers need solar power?
Portable traffic VMS usually run on solar panels and batteries. Our full-colour LED trailers run on mains power. If there's no power on site, we can put you in touch with a solar LED trailer partner.
Buy or rent?
For a one-off event or a short campaign, renting a screen trailer is often cheaper than buying. For regular use, buying can pay off. Our rental plans run from 10 days to 12 months, and the longer you commit, the less you pay per day. See rent or buy an LED screen? or browse our rental screens.
For more ideas, read 8 ways businesses and events use LED screen trailers.