Well my name's not Dave
but I feel qualified to answer the first part of your question Nigel
I may live just over the border but use these roads very regularly.
The proportion of high quality roads in Lincolnshire is small for starters. A little bit of A1 down near Stamford, a few bits of D/C and the rest is a mix of old Roman straight roads, joined by narrow, twisty bits. The only motorway is in the very north of the county. There are many B roads with better sightlines than the A roads. Lincolnshire is a heady mix of fenlands, where drainage ditches are sufficiently deep to drown people, and wonderful Wolds, where pockets of cold freeze the moisture and make for some 'interesting' surface changes in winter. The old drovers roads are sheer delight and virtually unused by the majority of drivers ...thankfully.
A lack of ability to drive according to the conditions and vary pace to suit those conditions is a major factor. Non locals will mostly drive according to the posted speed sign regardless of road type, whereas the locals will (sometimes) reduce speed appropriately. The non-local gets frustrated and overtakes without realising there is a slight dip ahead and meets someone head-on.
There are many villages on the NSL rural roads and people don't slow down sufficiently for the raise in levels of probability in mixing with more vulnerable road users.
As said before, many of the crashes are single vehicle, ran-out-of-talent situations, often lack of ability to judge and reduce to a safe speed followed by loss of control on corners that follow a long straight. I have been advised by someone in authority, that the majority of crashes occur at well under the posted limit and it is inappropriate speed for conditions, not speed alone which is the major problem.
You also have (as in the February 14 crash on the A52) foreign drivers going to and from agricultural locations, fully loaded with workers. If the crash had occurred a couple of hundred yards further west, it would have counted against Leicestershire not Lincolnshire.
The A52 changes in character from Boston to say, Bingham several times. In part it is wide, straight and flowing (apart from the odd cross roads which tend to catch out the unwary). It then becomes twisty, much narrower, with adverse cambers and hidden dips. After Grantham, the stretch between the A1 and Muston is particularly tricky. There are several open stretches, where the driver who plans well ahead and scans correctly could actually get an overtake in quite safely and satisfactorily but usually, everyone plays follow-my-leader for around 5 miles, particularly when following either a heavy or a plodder.
They then cross the border into Leicestershire, as a straight and inviting piece of road opens before them. They don't observe the two junctions to the left and a couple of unclassified and mostly unused farm-type roads to the right. There are regular crashes, often fatal.**
On other main routes, there are a great number of large lorries moving produce to the major cities. They travel at around 40 and the queues behind them are legendary. With very few safe overtaking opportunities and a lot of close following traffic, there are few situations for one to overtake safely. It only takes one rather impatient driver to attempt a multiple overtake and be denied a slot into which he could fit quite reasonably if people were driving thoughtfully - to create mayhem.
** I posted somewhere before that it was only a sixth sense that stopped me from becoming a statistic a while back. I was waiting to turn right out of our village on to the A52 eastbound. Traffic from the right was just coming into view from the left-hander. Traffic was non-existent from the left. A second check to the right and I still had plenty of time to turn in front of them but I just felt something was wrong with the 'picture' I'd captured on my first look. I realised that one of the vehicles in that first picture was missing! As there are no turnings, there could only be one place for it to be... on the offside of the road overtaking the group. If I had not had that curiosity, imagination, ability to re-wind a mental video, call it what you will...to work out that there was something not quite right with the situation, I would have turned right - straight into the path of an overtaking vehicle.
S