The speed limits in El Salvador are 40 km/h (25 mph) or 60 km/h (37 mph) in built up areas, outside built up areas all roads are limited to 80 km/h (50 mph)
All of the road signs for the main roads are Green with White writing and the local roads are Blue with White writing.
The main roads in El Salvador are either tarmac or concrete and they are all generally very good and reasonably well maintained. There are older stretches of roads in the the more remote areas of the country and the condition of these can be patchy but in general much better than in Guatemala.
Petrol at the time of writing was about 1 US Dollar per litre and it is sold in US gallons.
El Salvador has a very small police presence on the road and I never saw a police speed trap or a patrolling police car looking for speeding vehicles. There is however a high military presence in the towns and cities.
To buy a SIM card in El Salvador you just go to any shop with the mobile phone network sign outside it, Then you buy a SIM card which needs your personal details to be entered in to the phone in order to activate it, I was fortunate to have a local help me with this process.
Once the SIM card has been activated you need to buy a top-up in order to get internet. I paid 1 US Dollar for the SIM card and a further 4 US Dollars for a top up and this gave me internet for 14 days.
No vehicle insurance was required for me to enter El Salvador ad I could not buy any at the border even if I wished to do so. The TIP was issued to me for free for 30 days. I was able to cancel it when I left also at no cost.