My mind also wanders on too-familar routes, so here are a few things that I consider helpful or have been told about.
Having some (even minor) alternative routes may help; you may want a system for choosing which one to take based on which roads are busy.
Taking this to extremes you can map out your city (thanks Criggie; also see if openstreetmap can use the data, or play with veloviewer tiles)
Some goals to compete with yourself might also help -- they help you to concentrate on the riding even if not the traffic.
I tend to slow down as I lose concentration, so thinking about being quick helps.
The sheer physical effort of some of these helps to leave the thoughts behind.
Some goals could be: Total time Time between 2 points
(Strava segments, for example) Maximum speed on a particular stretch Getting up the big hill without stopping/in a particular gear.
Trying to keep your cadence (pedalling rate)
up is a good one - choose a lower gear than you might by instinct.
A particularly good goal if your roads are rough is to minimise the number of potholes you hit.
This requires you to know whether it's safe to swerve thus to know what's coming up behind.
Combined with this, you can practice bunny-hopping over damaged bits of road, or lifting the front wheel over even the tiniest cracks.
Alternatively you might try keeping count of how many bikes overtake you vs. how many you overtake.
This isn't one for me but making words/phrases out of the letters of the numberplates of cars that overtake you can help keep your eyes on the cars themselves.
I found my handlebar mirror helps -- once I got used to having one, glancing in it became a habit (and in fact with it I can see cars coming up behind out of the corner of my eye).
In turn, knowing that someone is approaching makes me keep up my awareness.
I assume you don't have headphones on (that would be a bad idea).
Practice using your rearview ears -- try to work out what's going to pass you next and how wide/fast from sound alone.
Some people like bone conduction headphones which at least don't cover your ears.
Count +1 for each car you pass and -1 for each car that passes you and you win when you get to +10.
-10 means pay more attention to the road (thanks Criggie)
bicycles.stackexchange.com/users/7309/Chris H
I've had a few close calls (mostly with other cyclists and curbs) when I got too used to a route.
Here is what I do to keep my focus on the road: counting cyclists (and their female/male ratio - to determine if it is Spring enough :)) practicing bunny hops on small cracks exploring new routes or trying to choose the one with green wave practicing wheelies on climbs if there are no cars around (I would have commented these to Chris's answer if I had had enough reputation.
Sorry for the separate answer.)
bicycles.stackexchange.com/users/31743/Balint
TL;DR - Do intervals .
Although I have a few different routes I regularly take to work, 75% of the time
it's just one route.
I find doing intervals very useful to keep the route interesting.
If you know the route, including hills, flats and descents well, you can really aim to go full bore a particular section of it and then switch the bits you go hard on.
Doing this also makes the slower rides on the same route more enjoyable and less painful!
I like to do efforts on a few of the hills I have on my commute, and though I ride them on a fixed gear, you could add another element by limiting yourself to certain gears for certain bits of the commute as an extra challenge.
Good luck!
bicycles.stackexchange.com/users/28934/Drew
Loss of focus during safety relevant routine tasks is a very common problem in occupational research.
An example of drivers whose route cannot be altered to make it more exciting are train drivers.
The method of finger pointing and calling (FPC) had been in use in Japan for decades.
The train operator points at all relevant objects, for instance signals, and says what they see (eg "proceed signal").
A paper by Bhuiyan et al
* also explores imaginary FPC.
Imaginary FPC is compared to actual FPC with optical tomography of test subjects in a driving simulator.
The paper suggests there may be some benefit.
Imaginary FPC is particularly useful to cyclists since we rather not take a hand from the bars in situations where attention is required due to an inherent risk.
It is conceivable a combination of actual FPC and imaginary FPC increases your awareness of safety relevant objects and agents whilst cycling.
*Published in IEEE Pulse, May 2016, a peer reviewed journal.
bicycles.stackexchange.com/users/30402/gschenk
Not a bad thing, Nzall.
I believe you have enteted a mental state people called "flow".
At this state you are most peaceful and creative, yet your attention is never drift off from the road.
This is a healthy and most sought after state of mind.
I experience this every time I am riding on my own on a familiar route.
Any issues I have in mind will come to light without consciously thinking about them.
If there are no issues some ideas about life will emerge.
I think people experience "flow" in other activitied too, EG, when cooking and joggng alone, and when they are skillful in it.
But flow is more easily felt in cycling.
Three conditions to enter flow; you enjoy doing the skill
you are familiar with the skill
you are on your own Next time
do nothing special.; just keep riding.
Your internal state will cleverly decide when you will enter the flow state again.
Interedtingly, if you watch out when you will enter flow, it won't.
Happy riding!
bicycles.stackexchange.com/users/31345/Asta L
I've found that when I'm used to a certain route while on foot or on the bike, I tend to have my thoughts drifting away and becoming less attentive, usually leading to dangerous situations and sometimes even accidents involving other road users. It's dangerous and I'd like to avoid it when I start to take the bike to my current job.  What methods can I use to stay attentive and not get distracted by my own thoughts while riding?
How do I avoid becoming complacent during my commute after riding the same route for a couple of weeks?
bicycles.stackexchange.com
<commuter>
bicycles.stackexchange.com/questions/46335
bicycles.stackexchange.com/users/11269/Nzall
Cyclists have a number of strategies to prevent complacency when riding a route regularly. These include counting various things  - for example male/female cyclist or number of cars that ovetake you -, doing bunny hops over cracks or damaged road, timing yourself over various sections of the route, try to work out what is behind you from the noise, among others.  You could vary your route to work to prevent boredom. Use challenges to maintain awareness of your environment and notice other road users or obstacles along the way. Practice using your ears and mirrors to be aware of the road behind you. Try interval training or practice different skills like bunny hopping over potholes and cracks.
You could vary your route to work to prevent boredom. Use challenges to maintain awareness of your environment and notice other road users or obstacles along the way. Practice using your ears and mirrors to be aware of the road behind you. Try interval training or practice different skills like bunny hopping over potholes and cracks.