Replacing single lane bridges

[Okey Dokey]

NZ Transit is undertaking to replace two old single lane bridges across the Waitaki River with two new single lane bridges. These are near Kurow, and connect SH 82 and SH 83.

I was quite surprised that anything other than a two lane bridge would be installed in this day and age. On their website, NZ Transit say they consider single lane bridges sufficient, due to low traffic volume and the extra cost involved in building a two lane bridge.

What do other kbers think about this in general? Our roading infrastructure always seems so patched up and short-sighted. Do you think it is okay to put up new single lane bridges on State Highways? Has this happened recently in other provincial areas, like the West Coast?

I'm interested in your views.

[idb]

I don't see it as a biggie personally.
I've never had to wait for streams of traffic across there.
I'm pretty sure they actually used to be road/rail bridges and you had to look for trains as well!

[Okey Dokey]

I'm pretty sure they actually used to be road/rail bridges and you had to look for trains as well!

Yes, that is correct.

Although these are the bridges I'm aware of, I meant my query in a more general way. Is this (single lane bridges built instead of two lane bridges) another example of short sighted roading projects? Does it save that much money? Someone in engineering or construction may know the relative costs.

I find single lane bridges "quaint", but just didn't expect that they were still being constructed...

[jim.cox]

NZ Transit is undertaking to replace two old single lane bridges across the Waitaki River with two new single lane bridges.
...
What do other kbers think about this in general?

One lane bridges are just accidents waiting to happen.

They dont belong on state Highways at all

Transit should not be building them - they dont save that much

Transit should be actively replacing all of them

It is just typical NZ poor engineering practice

[BOGAR]

From the point of view that a bridge hopefully has a long life and that there is always going to be an increase in traffic, eventually the single lane bridge wont suffice to the amount of traffic. But costs still need to be considered and the future life may be set to 10, 25 or 50 years and a estimated traffic growth vs cost is based on that. So if the bridge is only given a 25 year life (even though it would actually last longer) and the traffic growth in that time will not go above a threshold the calculations for a two lane bridge will not make the project viable. ( NOTE this is not 100% correct but hopefully explains what i see in my job with projects like these).

[Badjelly]

Transit should not be building them - they dont save that much

How much? Can anyone tell me how much a typical short bridge costs, one lane and two lane?

[jim.cox]

How much? Can anyone tell me how much a typical short bridge costs, one lane and two lane?

In myexperience, the saving is around 25% to 30%

[Ixion]

What is the problem with them ?

[BOGAR]

Struggling to find exact info but got this.
I think they are for single lane bridges

Standard bridge beams 6x26m Single pile and hammer head 3.5m $1.4 million
Continuous steel truss (concrete deck) 5x32m Single pile and hammer head 3.5m $1.76 million
Cable-Suspension
(Steel towers, steel truss and concrete deck) 20,120,20 Pile groups 3.5m $3.04 million

There are a menagerie of other factors that influence cost of options. (earthworks and piped services infrastructure are excluded in the prices above).

[Badjelly]

It seems to me single-lane bridges fit nicely into Ixion's programme oif making the roads seem more dangerous than they are, thereby encouraging observant driving.

I myself don't see a big problem with them if traffic volumes aren't too high.

[Badjelly]

In myexperience, the saving is around 25% to 30%

Struggling to find exact info but got this.
I think they are for single lane bridges

Standard bridge beams 6x26m Single pile and hammer head 3.5m $1.4 million
Continuous steel truss (concrete deck) 5x32m Single pile and hammer head 3.5m $1.76 million
Cable-Suspension
(Steel towers, steel truss and concrete deck) 20,120,20 Pile groups 3.5m $3.04 million

There are a menagerie of other factors that influence cost of options. (earthworks and piped services infrastructure are excluded in the prices above).

So, a bridge costs about $2 million, and single-lane saves you about $0.5 million compared with double-lane. That's a reasonably significant amount of money to me, and it may be better spent elsewhere in the roading system. So single-lane bridges on low-volume roads seem fair enough to me.

[sunhuntin]

i dont mind them if they are short [like say, 2 or 3 car lengths] but anything longer than that should be 2 lane.

[Trouser]

Have they replaced the single lane bridge on SH1 south of Cheviot?

Must be next on the list or are they saving it as a quaint reminder of the distant past?

[Kickaha]

Have they replaced the single lane bridge on SH1 south of Cheviot?

No........

[Ocean1]

I'm pretty sure they actually used to be road/rail bridges and you had to look for trains as well!

And traffic control was a train timetable nailed to the bridge.

Did wonders for literacy and numercy.

Nothing much for NZR's reputation for making the trains run on time though.

Then they went and spoiled it by putting red stop lights on them.