One of the cool stuffs you can do with your GPS is routing. It's not only that the GPS shows your destination point on the map, but it can also show and lead you the way to get there. Fancy ay?
Well, unfortunately based on my personal experience, in Jakarta (I mean greater Jakarta, ie Jabotabek) you can't rely 100% on the GPS routing for two main reasons :
First, Jakarta's traffic condition is unpredictable, hence each of you already has your own favorite route to go to some places.
Second, Jakarta's traffic rules may change from time to time.
Let's discuss one by one. The first reason; GPS route works using two linear approaches, first is by using the shortest distance and second is by the fastest (travel) time. Please note that the shortest distance is not necessary the fastest route, therefore you need to choose which approach you prefer. My suggestion is to use the fastest time approach.
The thing is, while shortest route is fixed, the actual fastest route is actually changed depends on time of the day. For example, I already have several different routes just from Lebak Bulus to Citos before 7am, between 7am to 10am, after 10am, on weekdays, on Saturday, or on Sunday.
I don't think even Garmin have the ability to analyse the traffic pattern! I believe Garmin will only consider the road size (small, major) and type (toll and non toll) to calculate fastest travel time.
Please also check your route preference/avoidance setup, for example do you prefer to take shortcut via small roads? do you mind taking a u-turn? do you mind taking the tollway? These setups will determine how the GPS will calculate the route for you. However in Jakarta this is very complex, I like to take small road, but not in all parts of Jakarta. Therefore, my recommendation is to avoid small roads, because you cannot be sure about the situation of that small road. However, do not avoid u-turn and toll road, because based on my experience, if you do not allow u-turn then your route will be extra long, while the toll road will help saves time (but not always).
The second reason; Jakarta's traffic rule is often changed. I'm not talking about the traffic rules in the major road, but more on the local traffic rules outskirts of Jakarta. This is not limited to the traffic signs, but also physical road barriers, traffic cones etc. Jakarta's traffic is so heavy sometimes the authority closed a u turn spot or put a barrier to prevent the traffic to make a left or right turn. For example, Tendean road from Santa towards Warung Buncit, you cannot make a u turn back to Santa under the flyover at Buncit intersection in the morning (before 10am?) because all incoming traffic is directed to turn left to Kuningan. I'm not sure whether Jakarta map data includes this time based traffic rule.
Therefore, this is my final recommendation for GPS user in Jakarta :
a. Use your own proven route whenever possible, most of the time that is the best route for you
b. Only use the GPS route on the section that you are not familiar with
c. Browse the GPS map before you follow a route, so you understand how the GPS will take you and analyse if the route is make sense
d. Always observe traffic rules and sign, don't follow the route if it's against the traffic rule (eg enter a one way street, make a turn where it's prohibited to do so). There's a possibility that the traffic rule has changed and you GPS map is not updated
e. Check you route preference and setup. Reset the setup according your needs and situation
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