Route planners calculate on either speed or distance.
For the quickest routes they will assume you can travel at the maximum speed of the route, so motorways will always be preferred as they have a 70 limit. A roads are maximum 60, but there may be streteches of 20, 30, 40, 50.
Even if the motorway is only a minute quicker, but miles further the motorway route will be the option offered.
I use google maps for directions: I like that there’s a thumbnail photo of each junction. I think it touches on M25 too. But sometimes it suggests something different because of road works.
From personal knowledge of visiting family just the other side of Chelmsford and preferring M25 to A406 to cross London (how desperate when dreaded M25 is the better option!!!), the M25 beyond the A12 turnoff is often troublesome, and it sometimes tails back and delays access to A12, causing me to take M11 and go cross country on A414 (no use to you!).
Now they have resurfaced the A12 and it's no longer like an African dirt road, it seems to be a pretty good road. Can't offer much advice once you leave A12, VERY long time since I went to Burnham, and that was solo car.
Once you are off the major trunk roads I tend to find Essex roads can be a 'wiggle fest', plenty of meandering and bends!
Monty mentions the A414. Last time we visited Burnham on Crouch we did go via the A414 to Maldon. But then we do live practically on the A414. In fact before the 1980s it ran right through our village. It's quite a good road most of the way, particularly now that the major road works in Harlow are virtually finished. It may not be the fastest route but if you don't like the M25 (I'm not that keen) then it's probably a good alternative. I did only go with a solo car though, as Burnham is a day out to us, we've never stayed there overnight. You could pick up the A414 off the M1 directly, but I would avoid going through Hertford before 09:30 or between 15:00 and 19:00 as it is a real bottleneck and always very busy at those times. There is a railway bridge that funnels traffic from a 2 lane dual carriageway down into a single lane each way. Hit that at the wrong time and traffic is down to a crawl!
I would turn off the A130 at Runwell and go towards South Woodham Ferrers (A132) and then onto the lower Burnham Rd ((B1010).
The A127 is the hunting ground for Basildon Man and his little white van and the Sadlers Farm roundabout ( A127/A130) is chaos as the battle to go to Canvey, or Southend or Wickford is a horror to behold
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