PROBLEMS Metalization blocking e-toll signals

PROBLEMS

Metalization blocking

e-toll signals

Different toll agencies report very different levels of dificulty with metalization of vehicle windshields, but most are aware of the potential for rendering a toll transponder unreliable or ineffective. The transponders of course have their own built-in antenna and the usual setup is for the transponder to be fixed with velcro to the inside of the windshield, somewhere around the edge. Any metalization on or within the windshield can block or distort the radio signals between the roadside equipment and the transponder.

Rudy Malobicky of PPG Industries (Pittsburgh Plate Glass), a leading windshield manufacturer, says his company has talked to several toll authorities and to car manufacturers to find ways of handling the problem. Their solution is to provide a metal-free area, maybe 3”x15” where the transponder can be placed. PPG and the technical staff of the Pennsylvania Turnpike have conducted tests following letters from leaders of the northeast Inter-Agency Group to the major car manufacturers.

There are several kinds of windshield metalization:

(1) a heat blocking film tradenamed Sungate incorporated inside the glass laiminate to increase passenger comfort and reduce the airconditioning load of GM’s class of large sedans the Chevy Caprice, Buick Roadmaster and Cadillac Fleetwood — have no metal-free area, many still around but no longer in production

(2) an in-windshield metal film that is also the radio antenna for the new range of GM minivans, including Oldsmobile Silhouette, Pontiac Transport and Chevy Venture in N. Am and in the Opel Sintra and Vauxhall Sintra in Europe, all of which are in current production with the metalized windshield and all of which have a metal-free area along the top next to the roof, distinguishable if looked at from outside at a angle

(3) a metal heating film installed inside the windshields of Fords in the late 80s and early 1990s to combat icing, notably the Taurus, Sable, Crown Victoria, and Grand Marquis, and Lincoln Continental. Corvettes also used a coating for solar heat reduction but this is no longer being used. It is distinguishable by a goldish hue.

(4) a variety of after-market window tinting films applied to the inside of the windshield by car owners themselves or by garages and specialty windshield replacement and car improvement shops

The first three treatments involve a fancy technique called vaccuum sputtering in which a 1500 angstrom thin layer of metal and metal oxides are deposited on one of the two layers of glass that make up the windshield so it is sandwiched into the middle during the manufacturing process. The metals and metal oxides may be of silver, copper, or titanium and these are most accurately called a metal/metal-oxide layer, though the colloquial term is ‘metalized’ windshield.

The fourth type, the aftermarket metal/metal oxide films, are built into a polyester sheet that carries an adhesive and is supplied with a tear-off paper backing. Such film is applied to the inside of the car windows, usually by trained installers — at a cost to the costumer for doing all the windows of about $150.

After-market tinting

Mike Duco of American Solar Tinting, a leading installer of window tinting in Baltimore MD told us his firm uses the metalized product almost exclusively nowadays, the older dye based film having been displaced by the metal. The tinting is a privacy thing, and its thermal blockage is negligible compared to the metalized film. His firm tells potenial customers the heating load on a car in the summer can be reduced 60% with metalized window tinting. He says a major source of the new business is dissatisfaction of customers with the new CFC-free refrigerants in new car air-conditioners. He says they just don’t have the oomph of freon, now banned by the USEPA.

Duco doesn’t think the aftermarket window tinting should be a source of problems in electronic tolling because they limit the metalized material to the top 5 inches (125mm) of the windshield. He says that all but the top 5” must be left free of any tinting film to meet federal regulations designed to prevent reduced visibility in dark night-time conditions. He says any customer with a toll transponder is advised to simply locate it down by the dash.

European regulations for visible light transmittance through the windshield are more restrictive than those in North America, says Malobicky of PPG. His company has major windshield sales into Europe. He says Europeans are increasingly installing air-conditioning in their cars as a standard item and along with this comes a customer demand for solar control with metalized windshields.

Circular polarization of the signal as used in Combitech equipment helps get the signal through. Bill Thompson of MFS said at a press conference recently that that active tags from Mark IV have less of a problem with metalized windshields than some other tags, presumably backscatter tags, but there will probably be arguments with that. On highway 407 in Toronto customers with metal are advised not to take a transponder. With the fancy imaging system available there, they are dealt with as occasional users and identified by license plate reads, but billed as if they had transponders. Some other agencies mount transponders externally on vehicles with metalized windshields, a move that brings other problems — theft and damage.

Carphones too will use

Greg Shipman of the GM sub Delco says that a further consideration is the near certainty that car windshields will soon house antennas for cellular telephone and other wireless operation via some kind of laminated metalization. These too will provide a small ‘window’ in which the transponder will have to be placed to allow good reception for tolling. (Contact Rudy Malobicky 412 820 8700, Mike Duco, American Solar Tinting, 410 844 010, Greg Shipman Delco 317 451 6113)