I'll give you an example from roadway projects. This is the process for a design bid build project.
The governing agency identifies the project need based on priorities and budget.
Timeline for the project begins when an engineering consultant firm is hired based on qualifications (no bid allowed for publicly funded projects in the US) to prepare the plans and the contract documents. Design and bidding process typically takes 1 year. This is for projects roughly ranging from 10mil to 1bil in construction cost. All regulatory permits are obtained including environmental approvals prior to bidding the project.
Contractor is hired based on low bid but has to have succesfully completed similar projects for that governing entity bidding the project . They don't just let amateurs win projects just because they bid the lowest.
Construction duration can wildly vary between 6 months to 4 years depending on whether it's heavily phased due to adjacent traffic and quantity of work. Every contractor wants to complete the work and get out as quick as possible obviously because time is money and there's usually penalties for not meeting the deadline. Delays occur because of unforeseen conditions (like finding an endangered bat cave or a burial ground, pipeline that wasn't diverted ), design errors, and overly optimistic forecast for construction duration (which is set by the engineer of record and the governing agency.)
I have never experienced a project that was constantly delayed in the US. It's seldom because as someone from UK mentioned here, before the project is sent out for bid, a lot of work goes into planning it here in the US as well.
I wrote all that just to give you some background on how things are typically done in well run City's and States in US. if you want to talk about delays, try and work in the middle east where everything is done in a rush. Ridiculous expectations on deadlines, half ass construction documents, zero permits obtained prior to construction and endless changes to scope. Being a contractor over there takes some balls and lots and lots of patience as you lose your shirt trying to finish the job and get the fuck outta dodge.
I've seen both sides and i can tell you that US knows how to plan and build. You always run into issues like everything else but it's rare that projects fall way behind. At least in public transportation . It just feels like it's taking long because it's in your face daily as you drive by it everyday.