This is a topic that can be divided up into three parts :-
1. Direct action against an automobile eg slashing tyres, putting sugar in the petrol tank etc.
2. Action against the road network eg broken glass on roads, sign destruction etc.
3. Indirect action against the general automobile user and industry eg anti-car leaflets, gas station vandalizism etc.
Together with these actions a goal, or reason, for these actions is necesary, otherwise it can be seen as mindless vandalisim, which will not gather any public support.
Use these methods to spread your message and remember that a good PR campaign can gain more support then one "media friendly" mindless car trashing.
1.Direct action against an automobile
A modern car has many new security measures eg infra red keys, car alarms etc but also more parts and electronics that can go wrong. There is probably more computing power in a modern car then in the Apollo rockets that went to the Moon.
As with all machinary a thorough read of the operating manuals will show all the weak spots that will cause malfunctions, eg if the infra red keys don't work how do you get in? If the petrol tank lock is broken how to open it etc. To download, or get hold of, the car handbook if you plan to target one car is always a good idea. All information works both ways - how to cause problems or how to solve them.
A competent car mechanic should provide some useful tips - if unknowingly!
One interesting way to make some money and mess up a car, is to cut off the catalytic converter. An interesting article in the New York Times, explains that you'll get a couple hundred US dollars for one, as it has platinum, palladium and rhodium in it.
The car's alarm does not go off so it can be removed silently. Stop a car and make some money!
Of course stopping one car from rolling will not save the planet, but it can be used as part of a concerted strategy. Eg The car owned by the local car dealership owner, or the Minister responsible for Traffic, or someone whose delay at getting to their work place will cause a disturbance eg a key holder who opens up a store etc.
2.Action against the road network
This will cause the biggest immediate problems and consequently the most media coverage and, unfortunately, the strongest Police response.
The road network, like any system, has it's weak spots. Just think of one set of road works and the chaos that causes, to get some idea of the scale. The modern society relies heavily on the road network for moving goods and people about quickly. Industries in particular require that parts and products can be received and sent in a timely fashion. A breakdown in this system causes loss of time and money. There, my friends, is the place where it hurts most - the Bottom Line.
Apart from physically digging up a road, there are many ways to hurt the road network. Think of it as a body with the roads as veins that pump automobiles around. One blockage can cause immense effect if it's in the right place. Bridges, major intersections and tunnels are prime spots to cause a major stoppage. A stopped car, a bomb threat, a sit down protest etc are ways to cause a stoppage. Normally a re-routing of traffic will clog up and slow down the surrounding area too until the stoppage is clear.
The traffic light system is one that is vulnerable to widespread problems. Being an electronic system it has it's weak spots.(see Wiki at http://en.wikipedia.org/wiki/Traffic_light for info.) The CCTV system for traffic monitoring too has of cause weak links. The chaos caused by a large scale failure of these systems can not be under estimated. Look into your nearest city's road infrastructure for all the details.
Large garages or parking houses can be also seen as potential places of action. The failure of a electronics system that controls entry and exit, or just the failure of a boom to lift up will stop many cars from leaving the garage/parking house.(see The Parking Network for example)
3.Indirect action against automobiles and the automobile industry
For those not willing to spend time behind bars, there are many other ways to hurt the automobile industry. Just by not buying a car is one major way. To actively campaign against more roads, parking spaces, garages etc will also help.
To not promote the car by refusing to buy toy cars for your children or not seeing car sporting events are other ways.
The motor vehicle has become such an invasive part of our society, that only when it's not there will people begin to realize the scale of it's damage.
