13km/L in rush hour traffic using a Vios is impossible.
I own a Gen 2.5 Vios and I tell you, 8km/L is possible. 7km/L even. My worse was 7.1km/L..

And that's perfectly fine. Why? My driving style is a factor. My route is another. My aircon level as well. And many others.
Maraming factor na nakakaaffect ng fuel consumption. If you want to achieve 13km/L, leave early to avoid traffic. Level 1 lang fan ng aircon, 10 o'clock thermostat, shift at or under 2krpm and don't do jack-rabbit starts. Also, pump up your tires to around 35psi. Also, kung traffic yan tapos 2kms lang yung travel mo, di talaga matipid yan.
My average right now is 10.5-11km/L with traffic. Goes down 8km/L if the traffic is really bad.
Bago palang Vios mo. Should get better after 5000Kms PMS. Also, mag-full tank method ka para malaman mo talaga average. Pag puro 500 pesos, di yan ganun kaaccurate