How can I strengthen a part of lawn that is sometimes driven over by cars?

We have a muddy gateway area in our field, and some muddy pathways that turn into a slip and slide whenever it rains heavily. For the gateway area we used a rubber mat with holes in, and for the pathways we used a roll of mesh that is lightweight and goes down easily with pegs that you push through by hand. Very easy and fixes the problem (at least for us). We bought these from www.duratex.co.uk Hope that helps.

Grass grown in those grids or pavements is just SILLY. I thought they'd be cool and tried LOTS of them. No way do they work. Great idea but heck, I've never even seen pictures of healthy grass grown in grasscrete! I vote for 3/8 minus crushed gravel and fines. Forget growing grass for any trafficked drive, path or transition area. With landscape fabric beneath 4" of gravel, edged with 2X4 pressure treated, scored for curves as edging...'Treks' is better but more expensive. Need to have a propane torch to soften for curves in colder weather. The gravel needs to be compacted. It is just not ever going to work to have grass that gets too much traffic (think super stadiums for baseball and football that replace their grass every other year). If you put big boulders in they have to be OBVIOUS or if there is any damage to someone's car because they couldn't see it before running into it, it would be YOUR homeowner's insurance that is compromised. Don't make yourself crazy using organics. Just being able to grow a lawn properly for a little traffic is a huge endeavor that costs more than just biting the bullet and creating a semi pervious solution. Clay turns into concrete just LOOKING at it...what do you think concrete is made from?

There is a lawn reinforcement solution, but it requires work to fit it. There are products generally known as cellular grass pavers - they are often found in places like hospital car parks and comprise a cellular construction, usually made of concrete for heavy duty areas like car parks, and the empty cells are filled with soil and sown with grass. Its a solution that was primarily created to assist with preventing flooding from too much hard surfacing - this arrangement means the area remains permeable to rainfall, is green because grass grows through it, can be mown, and will readily withstand car wheels and weight. In an area such as yours, where it butts up to an ordinary grassed area, the grid or cellular pavers must be laid at the right height, so that the grass, when it grows in the cells, is at the same height as the rest of your lawn, and can be mown over.

Nothing else will prevent the kind of damage you're talking about, other than replacing that edge of your lawn with paving on hardcore and concrete to take the weight, and you'd need to do that in a bigger area, from the edge inwards, for stability reasons. Cellular, or grass paving grids, will provide an alternative solution. Link here to one supplier - note that these cellular systems are also made in lightweight materials such as plastic, but they will not adequately withstand the situation you describe, you'd need something like the TruckPave or LIght Duty Grass Paver, or at least concrete : http://www.matsgrids.co.uk/40-truckpave-grass-paving-grids?gclid=CMO1tcblgtECFcyRGwodc7oIoA

There are other suppliers of these products and many of the suppliers will freely give advice on the best method to lay this system, along with how big an area you'll need to cover in order to keep it stable.

I would put some stones, so that they lift most of the weight of cars, additionally they help the car to move without slipping, so making a lot less damages to the nearby grasses.

Because the stones will be lower then the top part of leaves of grass, they are also not so bad, visually/aesthetically speaking. And I find a lot better then wet dirt. I find that also stone covered by grass will do most of the work, if there is not so much traffic.