Saturday, 4 February 2017

The Devil Is In The Detail

It is normally the case that it is no more expensive to do things well than do things badly and in the case of the "things" on our streets, this holds true.

I am sometimes called a "Kerb Nerd" and this is a badge I wear with pride because it is the little details which can make all the difference. Perhaps it's not make or break time, but those things which don't quite work can at best be an irritation to someone like me, but at worst they mean a scheme or a feature doesn't serve the end user properly.

A simple example is the humble pedestrian dropped kerb which I go on about all the time. The kerbs need to be flush with the road. The slope needs to be gentle and we need tactile paving. The various elements used to construct a dropped kerb cost the same whether it is done right or not. 

In my experience, our road workers on site are experts (in general) in installing the features we need. In fact, there are many craftspeople out there who take take the most basic materials and make them look good. I've even known people who will point the joints on the inside of a brick-built chamber as if it was a piece of art on show to all. Nobody will ever appreciate their quality of their work, but they take pride in their work.

I need to wag my finger at the designers and specifiers who all to often get things wrong. Even worse, they don't take sufficient interest and leave the people on site to try and cope with their half-completed drawings and garbled instructions.

But taking a step back from even that, somebody is paying for work to be done. Whether it is a public authority or a developer, employing designers and contractors costs money and so it is in everyone's interest to get things right first time. However, like with much in life, one gets what one pays for, and design and construction is no different.

If you want a cheap design, then expect to have something designed from the comfort of the office by someone given a cap on the hours they can spend on the commission. If you want a good design, then expect to pay for the designer to visit the site a few times to understand the layout and then for them to be able to spend enough time to make sure the scheme fits together properly. It's also a very good idea for the designer to be involved in the construction too. Price is an important consideration, but in any contract there really needs to be a quality component; and this goes for contractors too.

I keep seeing the same things when I'm out and about, so here are 5 more things which people seem to struggle with getting right - aka little pet hates of mine (in no particular order);

Kerbs on a radius
Unless you are going to the effort and expense of having custom-made radius kerbs, you will be using a set of standard ones. They are generally available in radii of whole metres, but not at 7, 9 or 11 metres - and some profiles have even less choice. Have a look at this data sheet by Marshalls for precast concrete kerbs to see what I mean.

When I see a drawing showing a radius of say 4.5 metres, I know immediately that it will be a bodge involving cutting kerbs to make them fit or by having open joints somewhere and it will look terrible. Specify either 4 or 5 metres - it is not difficult.

Sometimes, people try and use straight kerbs to form a radius. For 12 metres or more, its fine. You can get away with going down to 8 metres with straight kerbs, but any less and it looks awful. We have the right kerbs available and we should use them.

Lay-bys and build-outs
Kerbs again. Where a lay-by is formed or the footway is built-our, we will often see sharp points or internal angles. Again, it will look like a bodge. Sharp points will be tyre shredders and angles will make it hard to mechanically sweep the channel (as with the photo below).

The correct way to do it is with carefully sized and set out radius kerbs which allow a nice sweeping kerb line rather than those corners.

Small paving cuts
This is where huge amounts of effort get expended in trying to fit rectangular paving to curves and where levels change but where we cannot of course bend paving slabs! We end up with small pieces of paving which will end up rocking and moving which is no good to walk on.

The solution is to plan the cutting regime so that large pieces are kept and it is the small pieces which are thrown away. A pragmatic solution is sometimes to use small element paving in tight spots (block paving for example) which is formed from stronger units.

Double-sided signs
A classic example is the entry/ exit points of 20mph zones. Often, we see a post stuck in the footway with two separate signs (one saying "20" and one "30"). It is really quite simple to have the sign made double-sided and the fixings taken from one side with the post at the back of the footway. It just looks more tidy.

This takes thought as the side fixings need to be on the correct side and we will need to check we can get the sign post in. Compare with a "from the office" design, we'll just get a symbol on a plan with no care about positioning.

Silly sign posts
How many times do we see a traffic sign (often parking-related) on a post when there is a lighting column right next to it? Oh, it's just me who worries then! This is another example of people either not going to site or not thinking beyond their own little task.

There are limits on the size of sign which can be attached to a lighting column because of the effects of wind loading, but basic parking signs are small and we should use the things already on the highway for more than one job.

If we are being really dedicated, we can look at attach signs to buildings or walls. Of course, we need to get agreement from the owner, but it saves a post (which can end up getting hit, or the sign rotated) and it just looks so much better. Care should be taken that the sign can be seen.

Good design is about having time to think, about understanding the construction process and very importantly, the needs of the end user. The job of the highway engineer/ designer is to take the array of elements and techniques we have and to combine them in an appropriate manner. Good detailing takes effort, but it is essential for a useable and durable end product.


  1. Good design requiring thought is so true, but easily forgotten in our cost of everything value of nothing world. In Hatfield we have an excellent newish shared use pavement cycle route at the railway station which then ends at a dismount and push sign as the brand new traffic island is below cyclable standards. Great for my partner on her tricycle and hard on our tandem with the children. Good design rather than useless design please!

    1. In my opinion, cycle routes must be designed for tricycles and tandems - even better if the designers have actually ridden them; I'm fortunate as we've a tricycle and I have learnt a great deal from using it.

      I studied in Hatfield and I'm overdue a visit to look at some of the new stuff.