Making selected lines thicker to see overlapped features in QGIS?

Question

I have a bunch of overlapped lines. Some of the shorter ones are covered by others and are difficult to see. I am trying to see those lines by highlighting them via selection in the attribute table. However, the line in selection isn't wide enough to be visible from beneath. I can only see the selection if the selected feature is on the top.

My Question:

Is there a way to make the selected line thicker in QGIS (QGIS3)?

Related questions/answers here at GIS either do not address the thickness issue, or evolve coding and/or changing the line shape, which seems to be an overkill here:

Is there anyway to modify thickness & color of a selected polygon?

Representing overlapping polylines in QGIS

Shifting display of overlapping lines in QGIS?

Answer 1

In QGIS 3, you can use the Rule-based Symbology by

• going to the layer's properties -> Symbology,
• change the type on the top to Rule-based
• click the "Add" (+) button and add a new rule with the condition is_selected() = True as the Filter
• change the line style for this rule to have a different thickness (or color) as in the figure below:

Answer 2

If you install the Plugin "Expressions Plus" you have access to an isselected() fonction

Then you can use the data defined property to style your layer

for the thickness you can use :

CASE WHEN isselected( 'LAYER_NAME' )='true' THEN 5 ELSE 0.5 END

this will give you a thicker selection....

Edit : the Plugin "Expressions Plus" is not available for 2.99 but there is a is_selected() fonction already in 2.99 so no plugin needed for qgis 3.0