Thermoplastic road marking
Great Britain and Northern Ireland are well known for the excellence of the thermoplastic road marking the authorities take responsibility for.
This is definitely not the case with so many countries abroad where road markings are, if not totally absent, restricted to only a few in the centres of the largest cities.
Even in the United Kingdom there had been a very long period with no such driving and pedestrian aids. During the whole of the ‘horse and carriage’ age there were no road line markings, partly as a result of which there used to be terrible accidents involving pedestrians and carriage smashes that resulted in deaths and appalling injuries and disfigurements.
In the US state of Michigan Edward N Hines thought of and introduced road centre lines in the year 1911; subsequently, in the year 1917 Dr June McCarroll was the first to bring about centre lines on highways, In appreciation of the many motor accidents she caused to be averted the State of California named a roadway the Doctor June McCarrroll Memorial Highway.
The genesis of road markings in Britain was similar and possibly a follow-on from developments on the other side of the water. It was in Sutton Coldfield that centre lines came about in 1921, mostly because of protests about head-on collisions.
Subsequently, during the war against Hitler, the blackouts resulted in the people demanding more safety and, consequently, white lines came about on the sides of the roads to stop people straying on the roads during the darkness of the blackouts.
The question of yellow or white is hotly debated. In the USA yellow tends to be the colour of centre lines dividing lanes of opposing directions of traffic while white does that function with lanes of traffic going the same way.
The problem with yellow is that it has less contrast at night and the selected answer has been to use lead chromate to have a particularly bright yellow; lead chromate is toxic and workers applying it have to use precautions.
Paint is sometimes used for road markings. Frequently, it is combined with reflective glass beads, and sometimes not. Local authorities and private road owners think paint is cheaper than the other options.
In recent times, the relentless march of chemistry has brought about the rise of thermoplastic road markings.
They combine the technologies of:
- Hydrocarbons
- Rosin esters
- Maleic modified rosin esters
These materials are mixtures of:
- Binder resins
- Plasticizers
- Glass beads and other optics
- Pigments
- Fillers
The advantages of thermoplastic road marking over paint are:
- Increased durability
- Retro-reflectivity
- No VOC solvents
In large-scale applications specialised vehicles apply the plastic and melt it onto the road surfaces. The plastic is heated to about 200 Celsius and then poured onto the roadway. Some users then apply glass beads before the plastic sets. In small-scale applications the plastic is laid out in lines or whatever other shape is required and then melted onto the road surface by a type of hand-held blowtorch. This method is called hot-tape marking.
There are at present exactly three application methods in practice:
- Overlay. The substance is laid onto the surface and combined with the roadway or pavement.
- Inlay. The tape physically becomes part of the material beneath. Rollers combine the two together.
- Preformed thermoplastic. This requires the use of a propane heat torch.
- Epoxy has recently become an alternative to thermoplastic road marking.
